Since Joey's team won last time, Joey and Matthew could just tacitly agree to let Matthew's team win this time. So Joey could just forfeit early and both can avoid doing the task for any length of time.

Then next time again they could agree to let Joey's team win.
And the time after that let Matthew's team win.

So really they can just split the wins and avoid the tasks.

What's to stop them doing that?

The producers would cotton on, I'd imagine, and stop them from doing so.