I've looked into the fees to paypal myself 10,000 FROM my UAL card into my paypay account, then paypal puts it in my bank account, then I pay UAL card, but it ends up being way too much money, and I might as well fly somewhere and gain the real miles plus the UAL card miles
If you really want to shop get into consignments, or buying things in high qnty cheap and selling them on ebay or the likes, you may make a bit of money on the side as well as accumulating miles