Right! Generally this cooperation is either prearranged (between friends, one of which is high rated and the other low - perhaps with the high rated player acting as the lower rated one's coach) or not done at all.
It's hard to communicate with the speed and quantity required without using voice chat or the FICS/Thief partner suggestion feature (make a move on your partner's board and they get a chat with that move's notation). So random partnerships on chess.com probably won't succeed with this. On FICS, some high rated players set personal best ratings with this strategy, though.
You're assuming the 500 player actually listens to the 2000 player. If they don't, they're a solid 500 and going to do their unintentional best to die in 15 moves.