when i've reused a WHOLE yeast cake i've made a 1040ish beer and then come back and racked a bigger beer on top of it, like 1080ish. i've done this twice and it's worked fine for me, although i wouldn't say it's the best practice. i'll typically rinse yeast and make a starter again. if you're in a crunch for time, i wouldn't rack a beer on top of this cake, i'd save the brew day for another day when you can pitch the right amount of yeast...it's never fun to squeeze in a brew day in a few hours only to turn out beer that didnt' live up to your standards....i think this is also why a lot of people keep extra packets s-05 and notty around, for in a pinch circumstances. of course, you could toss all this out, go for it, and see how your beer comes out, although if you're brewing a smaller gravity and not as high hopped beer..i'd be a bit skeptical about how the beer would turn out.