There are a few things you didn't mention that might add to this conversation...
#1 You said he's about 280lbs. How heavy are you? Because if he's 280lbs. and you are 130lbs., well...there isnt' a whole lot you can do unless you are a black belt and he's a blue belt or lower.
#2 What are your experience levels? If he's a 280lbs. purple belt and you are a 200lbs. white belt, then you're likely gonna be out of luck because not only does he have you severely outweighed he also has you by years of technique.
With all that being said I belong to a gym that's "fortunate" enough to have some big boys. We have a 260lbs. monster that has ungodly strength, a 340lbs. guy, and a 390lbs. guy who's strong as an ox. I'm 200lbs. and I get to roll with them a lot because to be honest the weight gap is huge and I'm about the closest in weight to these monsters. When I first started I used to have severe trouble...I would get stuck under them (mostly in side control) and I couldn't do anything except sit there pinned to the mat for a while and then tap out from not being able to breathe. After doing this for a while I've picked up a few things and it's not as bad anymore.
Just remember to always keep moving, never just lay there, and if you do need to rest for a second never do so on your back...always on your hips. Constantly try to move and push for space, and every inch they give you fight to create a scramble. If you can force scrambles you have to use speed to get out and get to a neutral position. Most big guys like that are going to move as little as possible so they will give you some time to work and push and squeeze trying to make space...never stop fighting to get out.
One thing I'll do a lot with the 260lbs. guy is let him get mount...the way he's built in particular is pretty top heavy. If I let him get to mount he's not near as stable as some others. Normally once he gets to mount I can buck and throw him off balance enough to reverse the position. If he's got a good mount that day and bucking isn't working I'll throw an arm up and give him an armbar on purpose (he's kinda slow on his armbars from his size) and when he changes up I roll and work the escape to the pass.
Maybe that will give you some stuff to work on, but I'm still interrested in hearing you size and skill level vs. his...