As the subject says.....

I would like to machine some 2D shapes out of ABS sheet plastic, but I
don't know how to hold the stock while doing so.

I think some sort of adhesive w/ a sacrificial backer would be best,
but then don't know what to use. Something that I can stick it down,
machine it and then peel off the part and clean off the adhesive.

The only other option I can think of is vacuum, but that is a lot more
involved than the other method.

TIA

Jeridiah