Not only can't I think of any Vanguard mileage promotions that have ever been, I can't think of any Vanguard promotions in general (e.g. no deposit bonuses). It would seem to go against their low-cost, no-hype philosophy, anyway.

If you're interested in Vanguard's funds rather than the brokerage service itself, I suppose you could open an account at one of the other discount brokers and buy the funds retail through them. That, however, would probably be a terrible deal financially speaking due to the commissions.