Agreed.

Like I mentioned and Nev suggested, having Anakin in the temple would be the latest we could really see him.

If you had Mace go by himself, and cut the dialogue between him and Palpatine, maybe you could imply Mace went to align himself with Palpatine. That would help explain the whole “betrayed and murdered your father” bit. The only issue would be making it to where Mace was one of Obi-Wan’s students.

Otherwise, you would need to make a totally new character, or at least show Obi-Wan had other students.

How you would accomplish this, I don’t really know.