Stay more nights.... change your 10 nights from cheap hotels into suites to get the more expensive room rates, or rent out 10 rooms per night!

On a serious note - there is the refer a friend bonus (up to 25k, 5k per friend you refer who stays 5 nights - they get points too), but you'd have to persuade your friends to stay at the Marriott. You can also trade airmiles for marriott points (sometimes, depends on the program).

Are you signed up for the megabonus at the moment as well?

Just search the forum, it will give you plenty more ideas.