They might both get their wish.
The president is, of course, scheduled to speak on Monday (Labor Day) at the convention, right around the time Tropical Storm Gustav, which is expected to become a hurricane, hits the Gulf Coast. Fox News' Bret Baier reported this morning, "We're told, by the White House, there are conversations underway about [the] schedule, and whether [Bush] will, in fact, speak on Monday. They are meeting behind closed doors about the response, first of all -- they have FEMA Director David Paulison already active down there -- and the administration obviously very sensitive to this. But if this hurricane rolls in, and the timing is the same, you could see the president possibly not speak on Monday night. It's something that both the White House and the RNC are working on right now."
I haven't seen this reported elsewhere, but it's probably fair to say Fox News' contacts within the White House are pretty good.