You are able to purchase up to ten percent of the points needed to redeem an award. Purchases must be made in 1,000 point increments. You need to get a purchase form in order to buy points. I have not done this before, but I assume it will take some time to get the form and get the order processed.

http://marriott.com/rewards/usepoints/tranpurc.mi

Based on the size of your desired reward, you would not be able to buy that many points.