MMM... yes, that IS a sacrilege. Mandoos!
After all, I don't find it such an improbable idea... we know that Tolkien, for example, could not match the Shire-Rivendell journey with that in the Hobbit. (okay, now at least we get cast out to the Void both. After all, when I put my name in the Barrow-downs name generator, it came out that I am an "unwanted Vala"
) But if Tolkien knew what he was doing, there were two possibilities: either he referred to something we have no clue about (like "the kingdom of Monte Albo" in the White Mountains) or to some of those we know: the fishermen of Minhiriath, the tribes of Enedwaith, the Dúnedain of the North or some Northernmen (Beornings?!?) from the Anduin Valleys, even the Rhovanioners as I said before (Dorwinion; Lake-Town, Dale?)... maybe even Harondor (was it under Gondor at that time? I think not, but I don't know if it was enemy at that time - of course they served Sauron, but there possibly wasn't a status of war, or was it?). He could also mean the Elves... Remember that Denethor knew very well about Rivendell, although it was really far away.