it is possible to lock yourself out of the car using the trunk hatch - have the engine run, lock all the doors, unlock the hatch (with a button or manual pull), kroll out the car, shut the hatch...

OP never asked about how to get back in, so, this procedure does exactly what the OP asked for - locks him out of the car.

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E53 X5 4.6iS
147K mi - Sold May 2013
Tireprints left in:
USA, Nicaragua, Costa Rica, Panama, Russia

E53 X5 4.8iS built 2005-10-17
66200 mi - June 2012
96000 mi - June 2013
112000 mi - June 2014
OEM fire extinguisher
OE first aid kit
OE tow hitch
OE TV module
OE aspheric mirror
K&N air filter
black/white badges
rear camera
4-channel video recorder

Here is the list of things I have done to the X