I've seen numerous polymer handguns (Glocks) that were stippled using a wood burning tool, soldering iron, etc. The plastic on the Excalibur stocks seems to have a lower melting point, but the results are similar.
I used a wood burning tool and used the pointy attachment. Most places customize the brass insert, and they sell checkered brass inserts on ebay (about $30) which would probably have worked well too.
Here's my first attempt. Not worried about it being time consuming, but the point was too small and it displaced too much plastic. After I was done, I used a palm sander to tone it down a bit and clean up where it was too ragged. It worked, but I didn't like it.
I used the round/blunt tip attachment and went over everything. Then I used a palm sander to tone down any rough edges. It works great, but will pick up dirt if set directly in it. I may tape everything off and spray paint the end. Overall this pattern works great. I may try the plastidip down the road, but I'm satisfied with this. If you try it, you may want to lessen the heat, and maybe not go as deep. I think the type of plastic used in the stock didn't help, and a true polymer would have been better.