That sounds like a brilliant way to do it - currently I have all my empegged mp3's backed up on CDs in a cupboard. I could grab them, add lrc stuff and then replace tune, but what I actually do - as jemplode makes it so easy - is download an album, use lrctool and then upload them. It's pretty quick, but if the lrc tagging was part of jemplode it would be great if you could have an automated process:

grab file
tag with lrc info
upload file

where I guess the only bit in the middle which may be tricky is just ensuring the correct lrc file is attached to the correct mp3 file. As it goes through the album, maybe a proces where the app asks "track xxxxx, which lrc file to attach?" would work.

Nice idea if it's easy.