Another idea would be to randomly rotate and flip the board before starting the game. There are (I think) 8 possible changes, so it's very likely that at least one of them would give you an arrangement where no frogs are on top of each other. There's a little bit of information available from the options that weren't picked, but since it's random and rotations always happen, you won't know which ones were rejected because of your opponents frogs and which ones were because of the random factor. If none of the configurations work, just make both players replace all the frogs.