I'm doing it right now, actually. It is possible; there are clients out there that will pay for problems to be solved or for deep expertise. Even in the cases where they want a warm body for 3 months to a year, if it brings in enough cash for your other two partners to keep working, then great!
Outside of America this is basically how you have to do it pre-traction.
I think freelancing equips you with other skills (knowledge of the Big Three financial statements, ability to work independently, relevant laws, how to value a company etc) that will prove beneficial when it comes time to start a company.
Outside of America this is basically how you have to do it pre-traction.