Yeah, I know you can buy those red or orange plastic studs that are used to hold interior door panels on for 940/960/s90 doors.

But if you can't wait for one to arrive by US Mail, you might be able to salvage one that has fallen out of the door frame.

The pins I've seen have a similar failure - the "ears" or tabs that hold the stud in the frame hole have broken off, leaving 2 "legs" with a small gap between them.

Now, remember the small plastic picture hanger anchors that use a screw to expand them in a hole in the drywall?
for example, this - http://www.rona.ca/en/anchors-with-screws-0484214--1

That's the principle I used to salvage my door pins -
drill a hole through the length of the pin, place the pin in the door frame hole, and run a sheet metal screw through the pin, to force the "legs" away from eachother, keeping it from coming out of the door frame.

Use a very small drill bit first, to create a pilot hole, then use a larger bit that matches the diameter of the sheet metal screw. Drill the larger hole until it ALMOST goes all the way from the top of the pin to where the "legs" start. When you run the screw in, it will take care of the rest.