Very, VERY rare and difficult given how difficult it is to get fellowship in GI. You have to look at each institution's "research track" and call up each program you are interested and ask whether or not GI is an available option. In my institution, for example, fast-track residents comprised of 20% of each resident class, but none are tracking to GI, or even cards, for that matter. Unless you just got massive GI research experience under your belt, I wouldn't count on it.
Your best bet is to go to a residency program with good reputation, and try to apply to GI from it. It's an extremely hard subspecialty to get.