Maybe the Boba at Jabbas palace was a paid double for the real one while he was on another hunt. Jabba said no to him trotting off so he got someone to stand in but was killed.

Give aways that he was not the real Fett was his flirting with the dancing girls in the SE.

After the sail barge explosion the real Fett comes back to find his hired double lying on the sand next to the sarlaac pit, removes the helmet and puts in on. Camera angle from behind so we never see his face.

A simple line of "You can't find good help these days." Or throwing some credits at the body and saying "Job completed" line and he gets on a swoop and heads back to Slave 1 on the outskirts.

Would work for me.