As @Randy said, pins work. As is the basis for the flip jig.
I actually prefer to cut a pocket into my spoil board to have an accurate alignment and work piece holding.
I did a 6 sided job here.
Since then, I bought one .75"x4’x8’ sheet of MDF and ripped it to make over 30 pieces of 8.5"x11" spoils.
There is not one correct way to do this.
The ONE thing that matters most for any multi sided job is accurate registration for sides 2+ from the original job.