I've been giving some serious thought to this zimmers as it's something i'm thinking of doing.
My instinct is to take my audax bike with racktop bag on the train, cycle an A-B route, over several days, staying in B&Bs, and get the train back.
My thinking is thus:
The touring i want to do is in france, which means getting the TGV to "A" and back from "B", and a bitof research tells me that they don't like bikes on unless they've got the wheels off and in a bag. So you at least need to carry the bike bag with you.
Plus, I think wearing the same shorts for say 5 days is going to get a little uncomfy.
So therefore I need at least the racktop bag, the full panniers if i'm camping instead of B&Bing. which means i need the audax bike not the racer.
What you're suggesting would be possible on three conditions: (1) is that you're comfortable wearing the same shorts for however many days you're going, (2) that you can get breakdown insurance/some sort of rescue arrangement should a mechanical happen, (3) that you can transport the bike to "A" and back from "B", i.e. you don't need a bike bag or that you can somehow get it from "A" to "B" without having to carry it.
Further musing on these conditions:
(1) I've never tried it so I don't really know, but if you do try it and find it to really chafe it would be a really bind to have to turn back. You'd have to keep buying shorts and chucking the old ones away, which would make it more expensive a trip than you'd planned.
(2) You might need this anyway. Beyond punctures and broken chain, which can be fixed with what you can carry on the racer, what mechanicals are you likely to have?
Something like a broken spoke you'd be able to replace if you have chainwhip, cassette tool and spare spokes, they're no way carryable on the carbon blingmobile but possibly are on the full tourer, but anything else you'd want to have breakdown insurance anwyay. Broken saddle? Split wheel rim? Can't really recover from that very easily.
(3) You could, with a bit of arrangement and faith, post it.
Another possibility arises though: whatever area you're thinking of going to, you could simply have multiple bases and from there go out on round-trip rides, leaving your stuff at the base. From looking at maps, it occurred to me that you *might* be able to achieve a higher concentration of the good riding to the boring 'grind' - the interconnecting trunk roads.