Awesome about being an EMT! So are you going to be a non-traditional student by 2013?
Well in general, I would say, if you're going to still be in undergrad by the time you apply, I would just give them a heads up, even during the course, that you might ask for a rec letter in the future. If you're graduating undergrad and will be out of school 3+ years, I would ask for them now. Especially if your school has a rec letter service where you can store it for a few years.
You will be using these recommendations to comment on your performance as an undergrad, that's all they need to talk about anyways. You should supplement that with another 3 years down the road from your EMT supervisor that can comment on your performance after. Each rec letter needs to serve a purpose and paint a certain part of the picture. I didn't apply until I had graduated a while, and most of my professors didn't remember me, moved away, and the one that had written my past recommendations passed away. I didn't even have the 2 required science recs, but I think most schools overlooked it since I was out of school a while, but who knows, some of those rejections might have been because I didn't have the minimum requirement.