This uses the DDD Printable Wall Control System (github) to mount the sander. 

I have the Bosch 5" sander, but it seems like the hook & loop sanding pads are fairly standard which is what the mount is using. 

Use a good percentage infill to keep this rigid, at least 40%.

For the sidepieces, I used the included 1x3 side brackets. Use these 4x10x8mm pins to attach to the mount.

I'd recommend using the locking spacers facing the wall surface, I used two of the 1x6 size for the 5" version, and 1x7 would be needed for the 6". This can be used to lock in the mount using the threaded pin. 

I do not have a 6" sander to test, but I am fairly certain the geometry for the mount will be correct. Please let me know if it needs adjusting, I'll be happy to.