1. Libraries are the ****.
2. Symlinks (untested)
For #1, you can simply tell Windows to store that stuff on another drive- and it's seamless to the user. Great if the primary drive is something fast that you don't trust, like an SSD (my case). Also great if you have to wipe a drive due to some unrecoverable operating system problem.
I've used #2 to move games from their installed folders on spinning drives to my SSD, seamless to the game, operating system, and download manager (EA Downloader, Steam, Games for Windows Live). The games will run without issue and the manager will still keep them updated happily. I haven't used this to move operating system files around, but it would appear to work for anything in the Program Files directory, or the directory itself. Might try it with the /Users directory and see if it's an easier solution.
6D|| 24-105/4L IS USM|100/2.8L Macro IS USM|Canon 70-300/4-5.6 IS USM|24/2.8 IS USM|40/2.8 STM|50/1.4 USM|85/1.8 USM|
60D||15-85 F/3.5-5.6 IS USM|