This may not be practile for eveyone, but... Get a bass guitar. Even if it's just some junky bass. Use it for warming up, use it for stretching those fingers. Practice the same scale exercises you would use on your guitar on that bass... You think you have to stretch now? Just try those five fret stretches on a bass. ;)

I just got a bass a week ago, I find that I warm up on IT now. Makes the guitar feel like buttah in your fingers.