turn off the switch in the trunk when the car is at normal height..if your bags dont leak it will stay at that height.
That's the simplest way.
You could put in a switch in the passenger cabin in series with the suspension switch in the trunk.
With both switches closed, the air suspension will operate normally. With either switch (or both) open, the air suspension will be deactivated.
You will have to press 'reset' at the suspension warning from the message center though.