It should be possible to adjust the significance estimate down based on an assumption of continuous sampling less than the sampling size target. E.g. if you're aiming for a sample size of 100, and after 20 samples the split is 19/1 the current ratio is 95%, but that's not accurate yet, so e.g. it could be adjusted to the average between the two possible outcome extremes (99/1 and 19/81) and show 59% with low confidence. I don't know the statistics or if that specific method actually makes sense, but it should be possible.