Does your school not offer a composite or committee letter? If so, you should have this, most med schools expect it now a days...and in fact you will need to explain yourself if you don't have one.
If you have a composite, it's as simple as getting new letters to go along w/ it each app cycle. The composite requires 2 undergrad profs and 2 other letters. Thus, the hassle is taken care of.
If you don't have a composite, ask your university if they offer, through the career center or pre-med office, a composite service to alum. If not you will need to explain yourself to med schools anywho. In this case, most schools, regardless how long you've been out of college, require 2 professors (from any education institution above high school, eg college, post-bac, grad, etc.) and 2 others (employer, boss, EC president, some other professional, shadowed doc, etc). Schools ask for different numbers of LORs, but they follow the above format. Some schools allow you to send in more.