I’m not sure this will work every time, but Sharon’s Kadima party has risen in popularity since his stroke. From Haaretz:
If elections were held now, Kadima would win 44 Knesset seats – four more than in the first survey taken after Sharon was hospitalized. Labor dropped two seats (to 16), while Likud lost one (to 13) in comparison with that poll. No significant changes were recorded for the remaining parties.