Here's how we did it:
Jake wrote out his thank you message in his own hand on a 5x7 card.
Confused? I'll repeat. Trace child's letters right side up, turn over tracing paper and trace the lettering on the backwards side, flip the paper over again and transfer the letters onto the back of the adhesive backed foam so that the letters are the right way around.
Next cut out the lettering. When you flip it over onto the foam side, the letters should be backwards.
Next you'll need some printing supplies, so if you don't have an ink roller or a tube of printing ink (or acrylic paint), run out and grab one of each of those before continuing.
Squeeze a bit of ink onto a flat surface like a big paper plate or a sheet of wax paper (the latter being a littler trickier to keep in place). We actually do have a sheet of plexi lying around, so we used that. It was perfect. Use your roller to spread your ink around into a uniform layer, and until you have a good but even coating of ink or paint on your roller. Then roll it over your stamp until all of the letters are covered with a uniform coating of ink/paint.
Turn your stamp upside down onto a piece of folded card stock, and taking care not to move it around, push it firmly and evenly onto the card so that you get a nice, even print. Carefully lift the stamp off of the card. Adjust the amount of ink you use for your next print if you notice that your print is very light or too dark and a bit blurry.
Print as many cards as you'll need all at once, and let them dry thoroughly before writing your message inside. I asked Jake to write four or five cards every night for five nights until he was done. That way he still had time between homework and bedtime to play with some of those awesome toys his friends gave him. Thanks again, everyone!