Reinsman (Jeffers has them) bits have a few models that have 7 shaped
shanks, the shanks are set back so they can't get ahold of them. I know
they have one with a snaffle mouth.
Alot of folks have horses that get excited at the starts. The best
option may to be to just wait 10-15 minutes, until the other riders have
gotten out of sight. As he does more rides, experience may help mellow
him (or maybe not!<g>)
tracy