Z-joint glue-up

[Gary G™]

I'm making a coin display for someone.
The main board has a 30* bevel on the bottom so it leans back.
It's to be supported by a leg glued to the back which is beveled to match.
The rear of the leg is beveled parallel to the front.
How do I clamp this so the bottom of the main board and the leg stay aligned?

[JGrout]

make a secondary three sided opening in a piece of scrap ply or mdf  that can be clamped to the back to slip the leg into then clamp it packing tape for the sided to prevent glue from sticking to the fixture

[blackhat]

A shallow angled recess in the back would be a good bet.