A lot of you say it can't be done, but it is very possible, even with a finite bankroll.
First, find a very large starting bankroll, say 100 billion dollars, and go to your casino of choice.

Step 1: Place $1 on red. If you lose double the bet, if you win bet $1 again. Continue doing this...
How many people will read only the title and flame me, without considering my brilliant plan? Everyone who is scared of reading white text. <font color="white">...until you lose a total of $3, then take your $99,999,999,997 and go buy the casino, close it down. Destroy it to make room for your new, flashier casino</font>