Well, I am not trying to pad my resume. This is a conference I normally participate in. I had a great experience previously as an undergrad - Now, I want to help staff the conference as a recent graduate. Premed or not - this conference is very important to me, and I plan to participate. The themes of the conference are an extension of values that I believe in. That is all I will say on that matter.
At the same time, you should not pursue an activity (or attempt to squeeze it in) simply to impress the adcoms. If you are pursuing an EC for personal development, then it may be worth you while, and you may not want to "squeeze in" an activity. ADCOMS will see right through you if you are trying to pad your resume.
I would just take up a hobby, or travel to a foreign country for three weeks - After all, once you get to medical school, you will have little time for yourself.