Is it possible....

[Ofnuts]

The portable version is you best bet I think.

But if you want to get technical, you can try this:

• Check if you current version added itself to the system PATH (note value and remove if so)
  
• ZIP you current version (and its user profile)and uninstall
  
• Install new version in  a different directory
  
• Check if it added itself to the system PATH (note value and remove if so)
  
• Unzip the previous version in its original directory, and unzip the profile
  
• Create two .BAT files:
  

Code:

SET PATH=(add the Gimp directory back in the PATH
SET GIMP2_DIRECTORY={path to profile directory, obvious different for each)
/path/to/gimp.exe

• Create shortcuts to these files
  

• Check your file associations, they are likely set up to start the new Gimp.