I tried sculpting something in to the shield to work, and that didn't pan out either. I then decided to try my hand at some press molding to see if I could make a copy of the hand on the inside of the Thunderhsield and then somehow transfer that over to the shields I ordered.
In the past I have made molds of terrain that I had built/sculpted by using Easy Mold Silicone Molding Putty - available from Dick Blick or from Amazon - and had good resluts with it. I figured this would be a similar process, just at a smaller scale and without resin.
Get out two pieces about the size of your pinky finger tip. Mash em together like green stuff - do not worry about mixing it too well. When it is a uniform color time to get to work or it will set up. I have had this happen.
Break off a piece and press it onto what you want to take a mold of. No release agent needed. This stuff is kinda oily.
Let it sit about five minutes. Will be completely cured. Pull it off.
Mix up some green stuff. Pull off enough to just fill the cavity.
Mash it into the mold.
Let it sit for about 30 - 60 minutes and then pull it out with an exacto knife.
Glue it to your shield.
This whole process took me less than an hour from start to finish and I was really happy with the results. I know this bleeds over into the recasting/copyright/fair-use realm, but you just have to use common sense when it comes to these matters - don't cast whole pieces to avoid buying more stuff, don't resell the items, and use it for what it is - a modeling technique.