If you have a United account with even 1 mile you can do this....or a continental account that you transfer 1 mile to united.

Chase United MileagePlus® Explorer Card:50k miles after 1st purchase,up to 60k miles possible(YMMV) - Slickdeals.net

its for 50,000 miles after one purchase..I've already done it.

Like I said in the post above you have to keep it open for 6 months.