If you're really serious about becoming clinically fluent, the best option would be the Puerto Rican medical schools. They're all LCME accredited, so you don't need to worry about being labeled an IMG. Pretty much all your patient interactions will be in Spanish, and many classes will be taught in Spanish. But don't worry too much - all exams, books, and puts are in English There are three options:
San Juan Bautista School of Medicine: This is the smallest, school. It's very community oriented and has about a 50/50 break between students from Puerto Rico and the states.
Universidad Central del Caribe: Pretty much the same as above, except the breakdown is about 90/10 PR/Stateside students. UCC and Ponce are considered about equal in terms of quality.
Ponce Health Sciences University (Formerly Ponce School of Medicine and Health Sciences): This is where things get interesting. The school was recently acquired by new administration, and the new administration is looking at increasing the PR/States ratio from 90/10 closer to 50/50. They're also looking at changing the first 2 years into purely English, and offering Spanish classes to those students that cannot pass a Spanish proficiency exam. These students will then have to pass a proficiency exam before moving onto rotations (which are pretty much all in Spanish). But the school is in transition, so it's hard to say how things will turn out.
The fact is that you simply are not going to be clinically fluent be taking a Spanish class in med school, or by spending a month rotating in Latin America. While you might be able to get by, you won't be able to communicate without a translator.
If you have any questions, feel free to PM me.