Going to school might be a great motivator for potty training. Have you told him he can go to school there when he learns the potty?
Can you negotiate with the Montessori? IE if it is a part-time pre-school, can you hang out in another room just in case he needs a diaper change? When he is there seeing the other kids going potty, he might decide to learn it himself.
Another option is forming a "pre-school" coop. That worked very well for Mite when he was little. There were a bunch of us apartment dwelling moms, in a college town, all too educated to be hanging at home all day:^); so, we formed a coop that met twice a week. We took turns with activities and things could be pretty intense learning experiences.
I'm amazed that he sketches already! And the CPR thing is JUST darling!!! That shows such a level of intensity all by itself!
