I'm not sure this is possible unless you match into a six year program that has a research year built into the system. Maybe during that research year, you could pursue other interests as well. The vast majority of residencies work on a rotation system. So, who's going to do your work if you're gone for a year? How do you then proceed the next year, when other residents will then be in the rotations you skipped?

good luck, but I don't know of a program that would allow that, ever