A friend of mine broke his arm and I made him a get well card using the boy from Crayon Kids. For the cast, I used white Liquid Applique. You simply squeeze a small amount over the area you want to cover, let dry (overnight is best) and then when it is dry, simply heat with your embossing gun. The Liquid Applique puffs up, giving a 3-D look. It worked like a charm. I got the idea from a card I saw on this site. It was so long ago, let me see if I can find the card.
I found it! Here's the link to the card which inspired me:
Gallery at Splitcoaststampers