I tried this for about a week. I switched credit cards testing each at 50 bucks at a trime. My bank of america, Citi, Chase, and Barclays cards and Visa gift card all worked for points. When I was ready I came up with a plan to invest in 10,000. I would make 10,000 payment. I then purchased a second 10,000 on another credit card. The plan was to sell the original 10,000 on the same day the second 10,000 was going to go through. If you purchase during the open hours the trade should go through in two days. Off hours it takes 3 days. In all you figure stocks will be mixed some up some down and all you have to do is avoid being down by 2% total in the long haul.
However, after my second purchase, I was given a warning that they would watch my account. I went through with the sale of my first 10,000 but have been holding the second 10,000 in stock. I'm not sure where the limits are that will avoid detection but it is below that.