If it was me, I'd do it by extracting all the frames for each letter, and then using an image editor to do one frame of the whole word at a time. You'd do this by pasting one frame of each letter into the image editor and moving them into the right place.
Only snag is, you'd have to make sure that the letters are all aligned properly across all the frames - or otherwise, your finished GIF is going to have them wobbling about a bit. But maybe that's okay. There's probably programs out there that automate it though.