Let's presume that it's windy and rough.

I wouldn't abandon the your boat.

Single handed, sailing to the tip of his mast and grabbing it without damaging your boards or rudders or losing control
of your own boat will be tricky. Getting that close to anything when it's honking always is.

Carry about 60ft of some 3/16 line. A halyard tail will be about right. Have your buddy tie it to the forward crossbeam of the top hull. When he's ready to try to right, sail by and have him toss you the end of that line. Take a couple of turns around your rear crossbeam. Sail away at 90 degrees.

I strongly recommend you guys get righting poles.