Law 78 has now so antagonized all sections of Quebec society from moderate Anglo professors like myself through to trade unions and perhaps the whole of the French speaking Quebecois intelligentsia that Charest has run out of good options. He could simply recognize that the existing tax system could be pressed into play to pay for higher education. Perhaps even applying an education tax to the top two income tax brackets and taking up the space vacated by the Feds in terms of corporate income tax and capital gains. This would have the merit of broadening the base and providing intergenerational equity and some equality in the tax system. The down side is that it would effectively be a tax hike on a significant portion of his own base.
The second best option (first best at this point from the POV of the Quebec Liberals) would be to declare a moratorium on tuition fee increases and at the same time as declare a date for a fall election and attempt to make tuition fees the singular issue of the campaign. Admittedly, this would be a hazardous gambit but more so is a hot summer of persistent thunder..