I would love to have an answer to this question too. I recently redeemed 5,000 My Points for 5,000 Vacation Miles. My end goal is to get two $50 Marriott certs. Unfortunately, it seemed that I could not request this when I redeemed the rewards - there seem to be two steps. Much red tape! My first My Points redemption - I'll let you know how it goes.
Any info would be much appraciated.