With the focus on storing lots of data in the user's appdata folder in windows 8 and the tendency to use fast (but small) SSD drives as the boot drive, do you think that Windows 8 should during install specify the destination for AppData
Please adjust Variables settings and see if it helps:
1. Right click Computers, click Properties.
2. Click Advanced system settings in the left pane and switch to Advanced tab.
3. Click Environment Variables button, edit the user variables settings and point the “temp” and “tmp” folders to another location.
In addition, I think you can also try creating junctions: