If the CA is off making PA's or radio calls and I need some configuration change quickly (happens a lot during cleanup to departure), I'll make a hand signal and follow it up verbally when they get back. Works out fine. There is nothing that requires you to act that quickly. It irritates me when CA's get their hand up on the gear when they decide its time to put the gear down on my leg. I hate it even more when they just decide to put the gear down. If you really want it down that bad, ask what I think about putting the gear down.