Ok, so the 4 diaper pin method of attaching Nicky's shirt to his pj pants doesn't work. I don't know how he does it, but he can take off the whole ensemble while leaving all four pins in.
BUT tonight a sheer genius idea struck! And darn it! This better work!
I put him in long PJ pants, and then put a button crotch romper (couldn't find a clean onesie, but that was the original idea) on over the pants. I used 2 diaper pins to keep the crotch of the romper shut. I could also end up adding one pin to pin the outside of the romper to the waist of the pants under it if needed, but I really think this will work!
We'll keep you posted.