nope, can't help you with the warmouth... but
i DO know the absolute lightest bass i have ever seen. it is lighter than most guitars.
check on ebay and find an old Hagstrom IIB.
they were made in about the 60's, but you can still find them for under 1000.00. and the bonus is the sound! they have old hagstrom pick ups and sound almost as loud, and definitely as good as modern actives. shoot, they sound better... it is one of his favorite basses to play based on sound alone!
here is a picture of the one my son is currently using:
he loves it.... takes it to school and generally has no complaints with it.
PM me if you would like and you can come over and try it. i think you'll be impressed.
ps-edit... oh, and by the way, it IS short scale. he currently has a set of Rotosound 77 short scales on it (small guage) and they fit great.