What about Bobby Portis?
I know a lot of people liked him at the draft, and he has been regulated to bench minutes with Gibson and Mirotic playing ahead of him (as well as some guy named Cristiano Felicio, who I have not heard of before looking it up just now). Maybe something like our 2018 pick for Portis would interest the Bulls?
He has shown enough NBA skill to play in the Celtics rotation, and maybe even take over for Amir next to Al.