I just did the following:
1. copy and pasted the \Roaming\bandlab-assistant folder to my secondary hard drive at root level
2. deleted the original folder (had to kill the Bandlab Assistant process first, otherwise windows could not delete the folder)
3. started cmd with Administrative priveleges
4. typed: mklink /J C:\%username\AppData\Roaming\bandlab-assistant J:\bandlab-assistant
(I now see bandlab-assistant in the Roaming folder, but with the little shortcut symbol in the lower left corner of hte folder name, indicating that it's actually a link to another location
5. restarted Bandlab Assistant. Windows had no problem restarting it from the link pointing to the real location on my J: drive
I assume all this is going to work fine when it's time for a new download. If it doesn't, I'll copy it all back.