I've seen DJ Jackson take some big guys down, a lot of lapel and sleeve snap downs trying to get their balance off.
Plus, you can drop seio-nage anyone if the opening is there and you get deep enough.
With the gi it's not as hard, if you can get them moving then footsweeps work just as well on huge guys as on little ones. Plus, you can drop seio-nage anyone if the opening is there and you get deep enough. I've thrown some huge ass guys with footsweeps and drop seio. The seio-nage is a lot harder if they aren't also tall, however.
Yikes! I suck at that technique in general, but my spine hurts just thinking about failing that throw on a 350lb dude.