We figured out this weekend by chance as we were waiting to start a T with the livewell lids open: If you put the motor in reverse and goose it a little bit and keep backing up, it'll cause water to flow in through the overflows. Could be useful in a jam if you're pumps happened to quit working and you had fish and needed to fill your livewells...
At least it works on an 06 Stratos 201. Prob wouldn't work on every boat.