I am glad that you like my T35. Here are the steps, and I like to share the process.
1. You will need to unscrew four screws from below, but open the casing from top. I don't know if it will void any warranty, but you might be able to slide the front panel without opening but it's rather difficult.
2. Once you open the top cover you can slide up the front panel and peel the plastic cover.
3. Scan this on your computer to get the right button, and LCD position.
4. Fun part ! now you can create any pict from your dog, girlfriend, cars within the dimension of original T35 cover. Don't forget to mark the button position.
5. Print your result via a laser or an inkjet printer. I did mine on laser for crisp image.
6. Cut out the opening for LCD
7. Laminate the result with plastic or you can just insert a thin plastic book cover to protect the finish cover. No don't use lexan because it's too thick, and you will have a hard time to press the buttons.
8. Carefully reinsert everything into the box, make sure no cables are pressed againts the box cover, Done !
Attached you can find my other design.