Ok, here's a couple of ideas, including restating of earlier ideas:
(earlier): Allow as many classes as you like, but can't get off the boat til you have no more than 3 classes.
or... (earlier) Do a blank slate LR - wipe all record of what class at which level, and let the player choose them all until they hit the XP they were at before.
or... (dirty but shouldn't be hard to code, surely?) Offer the toon another +20 heart at the end of this particular LR which they must use immediately with Kruz's cousin Bruz on the boat, or lose. So the Ranger/monk/fighter can LR to pure fighter and take another LR immediately to go fighter/barb/rogue, and at the end of that they can LR again if they want to try something else. Let them go through iterations until they're happy, and once they decide they're happy with the build, they can get off the boat without the heart.
or... (earlier) excellent point about the LR being there to correct problems with the build due to the latest patch, not so that we can decide we're tired with our toons and completely change them. That's not what the LR +20 was intended for, was it?
Just spouting what comes to mind...