Our options for disabling local drives on the server today are as follows:
1. remove the 40-tl-mount-localdrives symlink
2. remove setuid from tl-mount-personal
3. remove tl-mount-personal altogether
Option number 1 is the "obvious" solution that fits in with how ThinLinc is configured but it's also unsafe since users can still run tl-mount-localdrives inside their session to mount their local drives. Options #2 and #3 are variants of the same thing - more or less crippling ThinLinc into not supporting local drives for all users.
It would be nice if there was a way for the server to disable local drives completely, for a user, group or everyone.
Looking ahead, I'm not sure how using FUSE for local drives would affects this.