How can FS force a Minimum call duration for a FS caller (someone calling out of FS)?

We have a carrier that penalizes us with a surcharge for short duration calls (sound familiar?).

So when a FS caller (not a call center or predictive dialer) calls a cell phone and gets a ring tone or calls an answering machine, the FS caller hangs up because they do not want to leave a message. But they do this in less then a few seconds after the call is answered. This becomes a short duration call and bang the surcharge applies. It is actually cheaper to pay for a longer call time (6 seconds in this case) and avoid the short duration surcharge. But the FS caller does not know this.

So, how can FS hold the connection to the called party open for at least the minimum amount of time I need to avoid the short call charge… even though my FS caller has already hung up the phone on his end? I would like to do this in the xml dialplan if possible.

Thanks

-Frank