Okay, this is a crazy idea and has no practical purpose whatsoever, but would you like to impersonate someone who is driving a stolen car? If you like pulling off pranks like this then this is the DIY guide for you. The idea is for the whole setup to impart the impression that you have stolen a car and are driving it with the screwdriver jammed into the ignition.
So heres what you need to do; visit a thrift shop or a nearby garage sale for that matter and get yourself an old screwdriver, which has the shaft of same thickness as that of the car key. Once you have the screwdriver you need to cut the shaft down to almost an inch long. Once you have achieved that, cut a slot that is 14-3/8 inches deep at the end of the shaft. The job doesnt require much of precision though. Once you have made the slot, round the end using a grinder or by making use of a file. This rounding allows for a smooth transition between the shaft and the key.
Now you need to check how far into the ignition your car key goes to work. Once you have marked that, add to it the depth of the slot that you have cut into the screwdrivers shaft and then cut the key as well. Also, keep in mind to use the spare key and not the original one. If your key and the shaft is an exact match, then thats perfect, otherwise youll either have to narrow the key or widen the slot that youve cut onto the shaft of the screwdriver.
When it comes to fixing the key onto the shaft; apply some flux on the key and then tap it into the slot located on the screwdrivers shaft. Make sure that everything is in order and then use a torch to silver solder the key to the screwdriver followed by the use of a grinder to get the edges tapered of the key. Sandpaper can be used for smoothening it and afterwards clean it in with a Dremel.
Keep in mind that this wont work for keys that have chips in them and also that having such weight hanging from the ignition is not a good idea for longer use. Nonetheless, its a cool little prank you can play on people!