Get to it Fred! My prediction is an announcement on the tonight show in early May. McCain is probably out by September citing “health reasons” and gives Thompson a strong endorsement.
I think Fred will go for a more dignified announcement at the Republican event before the Tonight show, and then discuss it on the Tonight Show.
Maybe not that early, but it's a strong possibility prior to the first debate. If Romney is tanking in polls by then, he may also withdraw and back Thompson, especially if there's a VP spot in exchange for him.
I think Fred would plan an announcement in a venue the opposite of that. Make it a big deal, but make a point about the location -- Independence Hall or someplace like that. It's clear he's trying to go about this in a different way.