How do you grapple with a training partner that's 300 pounds?



So I train MMA, and my stand up instructor is 6'2" and about 300 pounds. He rolls with us when we do BJJ. He's alright, doesn't have a belt ranking in BJJ or anything, and mainly relies on his size to lay on you until he gets something.

So how do I grapple against him? What are strategies you use against big men? I can barely get my ankles to touch when he's in my guard. It's ridiculous. The only thing I've ever submitted him with is a keylock when I somehow muscled him into side control and I've seen someone get an armbar on him from guard. I'm 160 pounds at 5'8" so you can imagine the size difference.

So wtf do I do?
Don't end up on bottom. Work from open guard if you do.
Try half guard to back climb. I haven't figured out much details yet but the following video can provide a general direction at least...

Works well for me. I'm lots of huge guys i hafta grapple with.

Even if you can't get to the back I think half guard is still a easier position to work on the bottom, cuz its easier to sweep.
4 months of training and a 140 lb disadvantage? Butterfly guard and hope you catch an arm or triangle. Otherwise I'd say you're screwed! lol
This guy doesn't sound the knowledgable. Learn a few sweeps really well, and he'll go crashing all over the place no problem.
Well whenever I roll with a big guy (anybody over 200 I consider a big guy, I am only 150 ;) ) I always try to snap them down and get around them, even if I don't get the hooks in they usually flip over and pull me into there guard so atleast I am not at the bottom of them.

But thats just me, I have only been doing BJJ for a couple months so my tactics might not be as good as some of the other guys on here
Crane technique. When used defense.
with my experience with big dudes they seem to be really heavy towards the top half of your body (while in your guard) so i try to arm drag through and get to the back.
and by experience in bjj limited. but i have rolled with a three or four big big dudes