Init string command pre configuration script for telemetry link setup


I would like to use satelite modem in order to call flight controller and setup serial link as a dialup connection. In order to do this I need to execute some script prior to serial connection has been established which has to send init commands to the modem in order to call to flight controller(ATZ, ATDTblabla and so on).
How can I implement such setup with qgroundcontrol without using any interim devices(like linux box with ton of scripts forwarding serial commands)?

Thanks for advise!