I agree that you should test rEFInd using a flash drive. I see one can download "A USB flash drive image file" containing rEFInd. I believe you would be better off using my instructions. If you have any problems with my steps, let me know.

Steps to Install rEFInd on a USB Flash Drive

1. Download "A binary zip file" from The rEFInd Boot Manager: Getting rEFInd page. I assume this will be saved in your Downloads folder.

2. Insert a flash drive into a USB port. Open the Disk Utility application and partition the drive as follows.

   

   The format of the second partition does not matter. I happened to use MS-DOS (FAT). Before applying changes, click the Options... button and make sure "GUID Partition Table" is selected.

   

   Apply the changes and quit the Disk Utility.

3. Open the Terminal application. Enter the following commands. You will be prompted for your log in password.

   cd  downloads/refind-bin-0.8.7
   ./install.sh  --ownhfs  /Volumes/rEFInd  --alldrivers
   

   This is what appeared in my Terminal window.

   Last login: Fri Apr  3 01:53:35 on ttys000
   Steelhead:~ davidanderson$ cd downloads/refind-bin-0.8.7
   Steelhead:refind-bin-0.8.7 davidanderson$ ./install.sh --ownhfs /Volumes/rEFInd --alldrivers
   Not running as root; attempting to elevate privileges via sudo....
   Password:
   ShimSource is none
   Installing rEFInd on OS X....
   Installing rEFInd to the partition mounted at /Volumes/rEFInd
   Copied rEFInd binary files
   
   Copying sample configuration file as refind.conf; edit this file to configure
   rEFInd.
   
   
   WARNING: If you have an Advanced Format disk, *DO NOT* attempt to check the
   bless status with 'bless --info', since this is known to cause disk corruption
   on some systems!!
   
   
   Installation has completed successfully.
   
   Steelhead:refind-bin-0.8.7 davidanderson$
   

4. When running rEFInd from a flash drive, I needed to introduce a 5 second delay. This delay was not needed once I installed rEFInd on my internal hard disk. I assume you will need this temporary delay as well. This is accomplished by editing the refind.conf file. Enter the following commands to edit the file in the TextEdit application.

   cd  /Volumes/rEFInd/System/Library/CoreServices
   open  -e  refind.conf
   

   At the bottom of the file, enter a line containing scan_delay 5, as shown below.

   

   Save the changes and quit TextEdit. If you get the following message, just click OK.

   

5. Restart the computer. You should boot to the rEFInd boot manager. The menu that appeared on my computer is shown below. (Hint: To get a better view, open this image in a new window.)

Steps to Uninstall Automatic Booting to rEFInd

1. Boot to OS X.

2. Open "Startup Disk" from the "System Preferences" window. The "rEFInd" text, under the external disk icon, should be highlighted.

3. Click on the internal disk icon representing OS X. The highlighting should switch to the text under this icon, as shown below.

4. Quit System Preferences, shutdown the computer and remove the USB flash drive.

What is next?

The icons files are store in the following folder.

/Volumes/rEFInd/System/Library/CoreServices/icons

It should be just a matter of substituting your icons for the default ones.

If you find any of this useful, let me know. The next step would involve installing rEFInd on your internal hard disk. I do not yet know enough about the partitioning of your internal disk to answer the questions I have. Mainly, I need to see the output from the commands given below.

diskutil list
disktuili cs list
sudo gpt -r show /dev/disk0
sudo fdisk /dev/disk0

None of these command change your computer. They only produce partitioning information.

I can help you if you've a live USB linux distribution, ex. Ubuntu.

1. Boot into Ubuntu live USB by pressing alt when upon restarting and choose EFI Boot.
2. Choose to Try Ubuntu.
3. Open Terminal by ctrl + alt + T.
4. Install efibootmgr by entering sudo apt-get install efibootmgr.
5. After installing it, check bootOrder and boot values by entering sudo efibootmgr.
6. Usually you OS X boot value is 0x80, please get your Windows value.
7. You can change booting order by sudo efibootmgr -o <comma separated boot values>.
8. Adjust your bootOrder assuming your Windows boot values is 0x01 then you should enter sudo efibootmgr -o 1,80 <- Windows first. So that your Mac should try booting to Windows first as you mention that you need an urgent solution.
9. Reboot to your live USB again and readjust the bootOrder by letting Mac boot into OS X first by sudo efibootmgr -o 80,1 <- OS X first.
10. Don't use any 3rd party bootloaders as you can easily adjust everything manually.

Advice:
Format your shared partition as ExFAT =)