The main questions are:

1. Is it the caramel mutation it's self that causes the tendency to kink?
2. Do any breeders really produce a large number of caramels with low (near normal) percentage of kinks?

As often as caramel kinking is reported, including wild caught animals and after years of outbreeding, I'm afraid it might well be that the tendency to kink is just part of the mutation like the color and can't be bred out. If the kinking where caused by a separate gene and not the caramel mutation it's self surely someone would have separated the two genes by now and produced a kink free line of caramels.

However, all is not lost if #2 is also true. Maybe all caramels have a genetic tendency to kink but some don't, why? Could there by some dietary or incubation setup variable that can greatly reduce how often caramels hatch kinked? It might be something unexpected like an extra vitamin in or not in the rat food or a degree difference in incubation temp.