They should just put a short lockout timer for withdrawing I think. Not 30 minutes like the penalty is for leaving, but something to discourage people from withdrawing over and over to try and get an in progress.
Like maybe if you que, you can cancel with no penalty if it is before the duty pops up, however if you withdraw after the duty pops for entry you get a 3-5 minute lockout. It would discourage this behavior.