With the NTFS filing system you can move folders such as Program Files (or sub-folders in it) to another drive, leaving behind a reparse point that points to the new location. Familiar to all *NIX users. I've done this on my sons PC and several others and it works cleanly and transparently.
Several good free GUI utilities to do this but I prefer
Junction Link Magic
I hesitate to post this because unless you know what you are doing and RTFM carefully it is possible to make a considerable Horlicks of your OS.
Mac