I was fiddling around as usual tonight with a glass of Makers Mark and a bunch of my HOn30/OO9 engines and rolling stock on a little pizza layout, watching a train circle for a while, then replacing it with a new train, usually with a different coupler type, and watching that for a while, and so on. While I was watching a train with the usual Micro-Trains n-scale couplers it hit me that I could easily glue track spike to the inside of the knuckle and use the same engine to pull all kinds of rolling stock.
So I tried it:
Coupled with a standard loop coupler Roco/Egger-Bahn/Jeouf-type skip:
Coupled with three links of chain:
And best of all, it still couples nicely with another Micro-Trains coupler:

I used a Micro Engineering spike (the smallest type available) glued in with CA (superglue). So far I've tested it on some very tight radiuses (about 4-5 inch) and it works with the loop, chain and MT coupler. It still couples reasonably well with McHenry n-scale couplers, but I haven't had a chance to see how it does in actual use (I don't have any cars equipped with McHenry couplers that can do that tight a radius). I also haven't tried out to see how many cars can be pulled using the spike before it falls off, knowing that the CA bond to the slippery plastic Micro-Trains uses for their couplers will eventually fail. It seems okay pulling five skips, plus the mod is easy and quick, you can just stick on another spike when the first one falls off. Also, for the record, I mount my Micro-Trains lower than standard n-scale on my Maine-type HOn30 stock, about 16 scale inches, which matches up with the Roco-type loop couplers nicely and probably won't affect the chain coupling much, but I haven't tried this yet with standard height n-scale couplers, (but I think it would probably work just fine).
And during the early days of railroading it was not unknown for stock equipped with knuckle couplers to have a slot cut in the knuckle to enable them to be coupled with link and pin couplers, so this is even sort of prototypical.
Good times!