Would it be possible to get a possession charge dropped with community service?

I really have to caveat my answer to you that it all depends. I see a posible defense in the fact scenario you gave us - but you need to talk to an attorney that has all of the facts. Fortunately, Virginia has a first offender program where the succesful completion would mean your charge is dismissed after one year. You have to complete 24 hours of community service, pay court costs and fees, be of good behavior and complete whatever drug program the community probation office deems appropriate (usually this is pretty light for a first time marijuana). However, while this charge is dismissed, it will stay on your record as a dismissal and cannot be expunged. So, if you have a defense - explore that option first. A good lawyer can really help you weigh your options.