Possible, but I would be to affraid of it tipping over due to it being top heavy...BUT... you could use the training skids and slightly modified the ping pong balls and cross arms.

Ideas:
Add more pingpong balls to the cross bars.
Seal tight the balls with expocy.
Move 4 balls closer to the body of the heli, maybe all the way to the landing skids to keep the heli from touching the water and keep the 4 balls at the end of the cross bars for support and balance while floating in the water.
Maybe use plactic wrap to proect the bottom of your heli from splashing.
Add more balls [X(] maybe even up to 3-4 per arm. I would personal do 4 to start off with.

Please Please some one try this and take a video. I can't cause my wife would KILL me.