Installation – Clean Install Without Formatting /home Directory

I cannot test this, but I think it's worth a try. Without logging into X, switch to a console CTRLALTF1. Log in, make a directory to store your current home directory, and then modify the account to move the current home directory.

sudo mkdir /mnt/tmp
sudo usermod -d /mnt/tmp/$USER -m $USER
logout

Login again without X. Define your home partition in /etc/fstab.

sudo vim /etc/fstab

It might look like this: /dev/sdb1 /home ext4 defaults 0 2. When correctly defined, mount it, make sure permissions are ok, modify the home directory again, and then move the files from the old home to the new home.

sudo mount /home
sudo chown -R $USER: /home/$USER
usermod -d /home/$USER $USER
logout

Log in again with X.

sudo mv /mnt/tmp ~
sudo chown -R $USER: /home/$USER/tmp

Does this work as intended?

OR

You can create a new directory, like /users. Mount the disk inside users. Change permissions on /users/$USER to match your username, and then change your home directory path with usermod.

I've done this quite often now - almost every time I did upgrade my system or (especially) if I switched to another distro. I normally log out, go to a console and log in as root directly (or depending on system configuration, as another user and switch to root), cd to /home folder and simply change my user's home folder name e.g. to "myUserName.bak". e.g.:

sudo mv /home/myUserName /home/myUserName.bak

After installation I can safely move all data needed to the newly created home folder for my user. (That's also a good point for thinking whether you e.g. really need that folder of big files you never touched the last 2 years ;) )

edit as suggested by comments: before you can access the files and folders from your renamed home folder you have to

sudo chown -R newUser.newUsersGroup /home/myUserName.bak