I had a flagrant in a playoff game a few years ago where a girl threw a punch during a scrum for the ball. It was a dead-ball flagrant, so I went T, then gave the baseball heave-ho. The observor at the game told me that, because there is no "mechanic" for a flagrant, this was the best thing to do mechanics wise.
I asked him later what would happen if it would be live-ball situation. He said merely fist for the initial foul call, and then the baseball heave-ho is the next best thing to do. This way, everyone in the gym knows that 1) you have a foul, and 2) you're ejecting the player. He specifically said DO NOT give an intentional signal.
There was a video posted on here (I think) w/n the last couple months that showed a live ball flagrant in a small college game, where the official I think did what I described above...
EDIT: I found the video on YouTube. Watch the far-side official.
http://www.youtube.com/watch?v=WubVH83-Auk