You might be able to get away with a cravat if it is fairly narrow. I think a big part of the appeal to the PC look is that everyting is very crisp and tight. Sort of contrary to a cravat. And I'm don't think a tie will look right with a PC jacket and 3 button vest.

If you could fudge a bit and go with a bramer or argyle jacket. A crail jacket would probably be the best to offer you more latitude on accessories other than a bow tie.