Just a note of thanks, my bud James "the 40k junkie," showed me this cool little trick and I like it so much I thought to bring it to you.
Step 1: Get some nice lego blocks and build them up like this. It is nice to have a base, but you don't NEED one. Sure, you can build this out of whatever, but I have two boys so Legos are everywhere.
Step 2: Build a house for the mold to sit in. I put a clear wall so I could see the GS filling the area. But it doesn't work that well, lol.. It looks cool though so I'll keep it.