Hard to beat a small petrol engine primer (squishy button) a 250ml bottle and some PVC tubing plumbed up to drop oil on the FRONT sprocket.
The primer is mounted on a convenient panel, a small push and a few drops of oil go onto the chain. Since it drops on to the front sprocket there's no oil splatter on the rear tire.
Uses ~250ml of oil every 20,000km ;)
O.K. I do have to remember to push the button now and then, but that's no big deal - has most of the advantages of an auto chain oiler with none of the downsides. i.e. it's positive pressure, I don't push the button, no oil comes out - so no dumping the entire bottle of oil on the ground - or on the rear tire. Need more lube ?, press the button harder.