hostap + ppp dialup question

[Vojkan Zivkovic]

Hi hostap community, I need your help!

I have the following scenario:

Raspberry Pi3 with built-in wifi is acting as Access Point using hostap, which is bridged to ppp0. I know it's 21st century, but this is a requirement! 
I have a wifi enabled device that connects to the Access Point. I need to trigger a ppp connection to dial out every time a wifi device is connected to the AP. 
Do you think this is feasible?

I appreciate your help on this.

Vojkan