Hi,
It's not really possible, this must be implemented in your logic. Expressing a condition change implies using a transition somehow, if you want to change the behavior of your feature.
Have another fsm checking for this transition condition and fire a event to that fsm, or change a fsm bool on that fsm, in the waiting state you can watch for this boolean value to change or implement that event as a transition to move to another state.
bye,
Jean