How about with options?
Make up a watch list of 10 stocks and you will have at least one ATM option double every day. Example: GOOG, RIMM, AAPL, SLV, USO, QQQQ, DIA, POT, GLD, NFLX.
Start = $1,000
1st trade = $2,000
2nd trade = $4,000
3rd trade = $8,000
etc.