It looks like we still have open borders with Charley. Don't forget we could send fast cavalry up through the HRE and then down on Vienne to save time -- but you were probably going to do that anyway. (The talk of attack on Pisa has me a bit confused though.)
Also, for the sea landing, why not land on the hill E of the target? It would give us a better defensive position. You might also consider just attacking the "Caduwatzit" city with just one or two rifles directly from the sea. I bet it hasn't got many defenders.
I'm having fun with my graphics program so will attach a completely useless map to make things more confusing.
EDIT: Okay, even more fun with a second map. I think maybe we can get all five cities in a reasonable amount of time. Given our unit technology advantage, I see no reason why a handful of Rifles on ships couldn't take both Camulodwhatzit and Gergovia very quickly -- especially if they are, as I expect, only lightly defended. I also think a cavalry force from the north can get Vienne in time to assist in the attack on the capital.