Why don't you find another alarm engineer and schedule a visit as soon as the new doors have been fitted,
The new engineer will provide and fit the required contacts,
Just inform the door/window installer that the alarm system is in service and not to loose/ bury the wiring if the main contacts have to be disconnected from their wiring(unlikely).
If a tamper alarm is created then enter your user code to silence the alert.
e manno, March 2013