MacOS – How to receive iMessages ONLY on the device you are currently using

No,

iMessage and FaceTime are linked to your Apple ID so you will need to add your Apple ID to the device, not your phone number.

If you send a message from the iPad it will use the Apple ID, so someone can reply to your email address, if they send a message to your phone number it will only go to your phone.

Right now OS X Messages can only receive iMessages sent to an email address associated with iMessages. So you'll have to ask people to send to your Apple ID email (or another one if you've got it set up with iMessages) if you want to receive them on your Mac.

There was some talk of Apple ID/phone number unification coming with iOS 6, so that an iPad or Mac could receive iMessages sent to a phone number, but that's not available yet, and from the publicly available information, it doesn't look like it's a sure thing either. However it's a possibility, you may want to pay attention when iOS 6 is released (which looks likely to be in September).