Frankly, the easiest choice would have been to make the U.S.S. Titan a Galaxy-class ship. The name fits well, it seems plausible that Riker would want to command it, and plus if there was ever a sequel to "Nemesis" (I know, I know...) you could have both ships of the TNG family onscreen together.
First of all, I would have preferred not to see Riker and Troi at all
in ENT's series finale. While the concept of someone from the future observing past events is a good one (and used to excellent effect in Babylon 5), Riker and Troi would have been my last choice for that, especially during the events of "The Pegasus."
Now with that said, if Riker and Troi absolutely
had to be in it, here's what I would have done: For "Azati Prime," I would have made the Enterprise-J the Enterprise-F, and set the Procyon battle in the early 25th century, and establish that Riker was in command of the ship even if we didn't see him. Then for TATV, we could finally see both him and the Ent-F, with exposition indicating he took command of the Ent-F after the Titan (there could be a little desktop model of the Titan in his ready room or something). That way, we have links to the ship from Azati Prime, to Riker's original intent to command the Enterprise, and the name link to the NX-01. Then use the idea you came up with about the Romulan peace mission, and we'd have a true winner.
I myself didn't mind that Riker and Troi were in the ENT finale, but wasn't exactly crazy about it either, if you know what I mean.
But I suspect that even if you're idea was suggested, it probably would have been turned down out of hand, due to having to design a new Enterprise, which would only be used for one episode. True, they could have gone with making the F a tease like they did with the Ent-J, but I'd think fans would have expected more, as we are talking about the Enterprise after all. I'm sure that the executives didn't want to have the Enterprise-F designed quickly, only for the fans to be unsatisfied with it, and they sure weren't going to give a lot of time to design a brand new ship (let alone the interior), so... Even though I agree that it would have been a better idea, it would have also taken more time and expense to execute properly.