Another method to make a spacer is to trace the back of your A2 stock on a mouse pad and use Shoe Goo to glue several strips of mouse pad together until you have the thickness you need. Then tape that to the back of your stock. You will need to add .75" to 1" to put the stock pack in a position that the charging handle will clear.
Of course this really only works if you need extra length of pull on your A2.
I like the foam pad idea and there was a group buy going on but I can't get a response. I've searched and can not find a similar product. Wouldn't matter if i had to cut the shape myself.