You can literally give them a task that will take a couple of hours to finish (like "port this library to language X, start by porting the tests, don't stop unt

You can literally give them a task that will take a couple of hours to finish (like "port this library to language X, start by porting the tests, don't stop until all of the tests pass against the new implementation"), go out for lunch, come back and they'll have finished and probably got it ~90% right.