I dont know if this will work, but try this.

Once the entity is placed, do a "c_rotate" by 360 degrees in all pan/tilt/roll directions.
Check the result for collisions, and reset pan/tilt/roll to 'correct' if there was a hit.

May work, but only if there is some poly to poly collisions.
If the new entity is ENTIRELY inside an existing one, it will possibly fail to detect.

Testing is the only way....