If you're serious about floating your X-Star Premium, consider the WaterStrider system for the Phantom 2. Tell them it's for the X-SP & ask for the crossbar to be left unglued so you can fit it without stressing your orange legs.
The quad flies a little differently with these floats, I get a little pendulum effect, but I'm sure they are more efficient than the DIY options I was contemplating.
Whatever floats you choose to use, be sure to takeoff straight up & land moving straight down. Any input from your right command stick can cause the bird to flip.