regarding the issue of short stature and school... if you still really are interested, could you still check with even part time preschools, and see if they could help with the issues related to causing GI issues? DS is also small and the school he is at now ended up getting steps for the bathroom because he could not go to the bathroom otherwise. When DS was three, he was not the only smaller size child so they had stools/boxes for the in class bathrooms even though the toilets were already kid-size. You can ask how they would address his frequent BMs.
But to use the bathroom, I am not sure I understand why he would have to be full disrobed so that may complicate it if he really has to go without his shoes. For pants, we use pants that are easy to pull down (i.e. no zippers nor buttons) so that DS could get to a toilet quickly when he needed to use the toilet (teachers understood that even at 3, kids may not realize they need to go until last minute - and the bathroom doors are always open so the kids could run in anytime they need to). And I have seen it all the time in the 3s room where the kids could easily get their pants/skirts down to use the toilet but would come out to ask teacher to help them pull their clothes back up, so I doubt he would really stand out with his motor skills.
Heck, even at 4, we still see occasional wardrobe misfires big time with backwards clothes, underwear peeking out the bottoms of pants etc (he forgot one leg).
