So I made a pilgrimage to the place where (practically) all the tools and stuff come from China and are cheap, and ran across a miniature lubrication pen that looked good, at only two bucks. Got it home, looked at it more closely, saw that it was basically a replica of a technical drawing pen, with a small tube with a wire inside it, the wire attached to a weight inside the nozzle. Fairly crudely made (in India, not China), certainly not crisp and precision-looking like a Rapidograph or Mars, but it looked usable.
One problem was that the wire didn't protrude far enough from the tube to do any good, so I took it apart and ground the tube down on a sharpening stone. For some weird reason it didn't work at all until I almost destroyed it out of frustration by slamming it down on the workbench; after that it worked fine. (I must have just missed smashing the nozzle.)
I recommend this oiler to any model railroad types with locos needing lubrication. I have a couple other oiler pens, and this one actually has the finest tip, perfect for dispensing a tiny drop of LaBelle or whatever potion you like to use.
For some reason, this item (#98850) isn't listed on their web site. It is, howerver, in at least the store I went to (in Newark, California), so is probably in other stores as well.