It is possible to keep the OBD port awake by sending the following:
Payload (hex): 02 3E 00 00 00 00 00 00
This is telling the GWM that there is a tester present.
Note: Caution this will cause all ECUs to remain active on the vehicle and cause excessive drain to the 12V battery.
Note 2: It also seems to overcome the issue that causes the alarm to set off if the BCM is queried. If you send this the alarm seems to be disabled for network queries (still works for other activities).
Note 3: The car will resume sleep after 40s, so send this message every 5s or so. It will also not wake up the car properly if it has fallen asleep, so you need to send this before the car sleeps to keep the GWM active.