AutoHotkey is reasonably easy to use. For your purposes, just find another key that you want to use as shift, and then make a script that contains (example is using the Windows key as the shift key, only while in Spring)
#IfWinActive ahk_exe spring.exe
Then either right-click and run it, or compile it into an .exe file and run that. Bonus with the .exe is that you can put it in the Start Menu/Startup folder and have it always running whenever you restart.