I am no expert, but what I read when I bought my clowns was that as long as there is an obvious size difference the female has a good chance of leaving him alone and later pairing. She will threaten it and the smaller fish should do the little submissive dance (more of a siezure). If she resorts to openly attacking it I would remove the new clown.
When I added my clowns, I bought 3 very small clowns with the objective of having 2 of them pair up. About 2 weeks in my tank, there was a clear dominant clown. 2 weeks later 2 of the 3 had pair up and started chasing the 3rd one. My original plan was to extract the 3rd clown and sell him, but by the time I was able to catch him the person no longer needed him. Things have settled down now and he stays on his side of the tank and the other 2 stay on their side.
Good luck.