A far easier way to make this happen would be to have him run a much better campaign in 2000, pushing the Liberals to a minority and resulting in the Alliance, PCs, and Bloc combined holding a majority of seats. As has since been revealed, the three parties had discussed forming a coalition government had this scenario had occurred, so had the Liberals lost their majority in 2000 Day would have had a pretty good chance of becoming Prime Minister.
I don't see the government lasting long, though. Even if the Bloc isn't actually a formal part of the coalition (itself a problem as the government would almost completely lack Quebec cabinet ministers), the policy differences between it and the other two parties make me think the agreement would fall apart pretty quickly. Plus, there's also the problem that Canadians might not like the fact that Day formed a coalition at all (for example, look at the outrage caused by the attempted Liberal-NDP coalition in 2008).