I drop seo nagi'ed a 240lb plus ultra in Phoenix this last year with ease and I was a LW.
The thing with the big guys is that they know they are big. They know they have the weight advantage and they basically want to use it. They love the "fat guy" trip to set up their timber into side control where they use their weight to push your far arm into a kimura/americana. So I just use that mentality against them.
I know the jerk/snapdown is coming and stay light on my feet for it. Once it inevitably comesin, I don't resist it and let that movement set up my drop seo nagi. I mean they ARE lifting and moving their own arms practically in the same way that I would be trying to setup the throw anyway, so I just use it to put me into position to drop.
As for landing on you, the weight it nothing. You should be so deep on them, so quickly that they are not going to be sprawl out on your drop. Their body will be so far foward, past where you are, that the only weight you will feel is their legs as they slide over your head.
I understand - but I think until I get good with it, I'll practice on small people.