I'm looking at it now (I've never chosen the 'use imported addresses' feature in the beginning, the other modes don't have importing menus).
I'll see if Electrum can work with a few hacks. If it does, I'll test it with a couple of thousand watch addresses / privkeys.

If it doesn't work out, I will likely post a job (but I will recommend using bitcoin-ruby for it - seems to be a better choice).