tufta08
Look into the Hamilton program:
http://www.hamilton.edu/academics/hcays/
It is quite immersive with homestay living arrangements. The courses are all in Spanish with a good selection of courses specifically for the US students and the option of enrollment in any course for students with sufficient fluency. So, this would offer the opportunity to inch towards the direct enrollment approach without all of the challenges. As far as study abroad programs go, this one is at least a bit rigorous academically.
This is a competitive program and they do favor full-year applicants, so I'm not sure what the odds of admission are.