According the to the Full Tilt FAQ on Rush Poker, you should not be able to save money by slowing down your play around "bubble time":
"You’ll post the big blind upon joining a Rush Poker* game. After that, the big blind is assigned to the player who has gone the most hands without posting it. If there is a tie for who has gone the longest without posting, the big blind will be chosen randomly among the tied players. All other seating positions, including the small blind, are completely random from hand to hand."