sapphire1: As kelea mentioned, it is the overall credentials that determines the fellowship award. However, I am reasonably confident that a high GMAT will be the most important factor of all, especially anything higher than 730 will get anyone over the hump and put him or her in that 30% bracket of getting some type of fellowship.
Moreover, as folks decline their offers and go to other schools, those awards will come back into play. So, if I were you, I would get in touch with the adcom a week or two after the May 1st deposit deadline and convey your interest and need in a diplomatic way. Nothing is guaranteed, but there is no downside to making a polite request.
By the way, I would not mention anything about others declining and making a case for yourself. I would not play that "entitlement" card, as it is very similar to something like myself going to UCLA adcom and asking them to admit me from the wailtlist as I know many folks from here have already declined their admit offers to UCLA. It may backfire, just my two cents.