I understand the Econ major a lot better than I do pre-med requirements, so I can give you some useful links.
First, the Columbia bulletin describes every summer class being offered this year:
CU Directory of Classes (it's not working well tonight because of some technical issues.) I know some people do them but they tend to conflict with internships, so a lot of people prefer to avoid them. Also, if cost is a concern, summer classes tend to get pricy.
Economics & Mathematics is a sort of joint major. It is meant for people who are essentially double-majors in Econ and Math but don't want to take such a huge amount of classes. It requires only a couple of classes more than the usual Economics major, but the requirements are pretty different. In reality, it is not really a track like the other 3. It is a unique major that contains both the Economics and Mathematics cores.
You can find more information about the major requirements here:
Economics and Mathematics Major
Note, you can click the four dimensions to get detailed descriptions of the requirement. By the way, this site:
Program Planning in Economics has links to similar explanations for all four Economics tracks.
This link has the commencement program, which lists every single major this year's graduates completed:
Commencement 2009 - Barnard College . Note that there was one person who double-majored in Economics & Mathematics and Physics. There were also plenty of joint program, double majors, teaching certification, etc. graduates. It's a good place to look for ideas on what has been done.
Languages are really popular as minors, too. If being pre-med is a priority because you want to go into health administration or policy, then that's certainly something worth considering.