So I just got some shorty batteries for my 22 and would like to run them in the forward position.

What do y'all use for spacers?

Use some foam blocks. My LHS does paintball and airsoft and I picked up some large EVA foam blocks they use to keep lipos from bouncing around in airsoft guns and cut them down to fit.

The AE SC10 foam spacer is a good way to get a decent chunk of foam that's already battery width as well.

Find old flip flops and cut them up....

If you kept boxes for products you bought (i.e electronics) you might find something useful.

I cut up that anti fatigue mat.