Start PPP connection when sensing connection on a port using napt

[FIAV1]

Hi guys, I'd like to start with a scheme to make things clear:

Sensor <--serial--> ESP8266 <--wifi--> PC

I'd like to know if there's a way for starting PPPoS connection from ESP8266 (client) to Sensor (server) in case PC starts a new connection to ESP8266, using LWIP napt to redirect traffic coming from PC to Sensor through PPPoS (something like a bridge).
Translated to steps:

• PC connects to ESP8266
• ESP8266 something sense the connection and starts PPP
• when PPP is up, data is sent to Sensor through PPP (thanks to napt mapping) and backwards to PC

In case nothing suites this use case well, do you have some hints to get me on the right path?

Thanks a lot!

EDIT: I found out that the lwip’s ppp module already has a file called demand.c that’s useful for this purpose, but I dunno how to implement this right, any suggestion?