What's the best method to simul reveal in an email game?

I need to figure out the process so that both players reveal air support at the same time but be able to do so in an email game.

Gentlemen agreement and overlapping logs: in first log player A says

“I am to reveal my air chit in 3”
“2”
“1”
and he reveals his air support.

The above log, when opened by player B, would call for him to start an overlapping (i.e. his own) log; this way he can react to other player’s actions. In this particular case, after A says “I am to reveal my air chit in 3”, he would play his own chit.