You can often find lyrics to the songs on piano rolls by searching
on-line.  Sometimes it takes a little searching and some editing to
find a version that fits the piano roll.

I wrote a program that allows you to add lyrics, from bar based text
listing (pretty much automatically) to a MIDI file.  It is pretty
easy to run the program to see how well the printed lyrics match the
arrangement of the roll.  The only listed roll that I have as a MIDI
file is "I've Got Rhythm".  I could add lyrics to it if anyone is
interested.

Best regards,
Spencer Chase
Garberville, Calif.
http://www.spencerserolls.com/