I bought a multi-pack of post-its. Make sure your colors coordinate well. Honestly I don't remember the exact price of the post-its. Not much, couple bucks. Now you can just peel off the back piece and stick it on the front of the frame but I added a little double sided tape on the bottom half of it too, just in case. You don't want your gift to have the main piece fall off. Lame. So do that, center it and stick it on the front.
Got the smart stuff ; )