I also wanted to do envelope liners and came up with this really neat idea of doing a word jumble with words that have to deal with our wedding. I just copied and pasted about 30 or so words using Microsoft Word. I used different fonts, font sizes, and font colors for each word or phrase. I then printed the word jumble. Then, I traced an open envelope onto the word jumble. I then trimmed 1/2" from the bottom of the envelope to make the liner and here's how it came out...
I used permanent double sided tape to adhere the envelope liner to the actual envelope. Here's how it turned out...