I've just made up a pretty elaborate one for my SuperDuke.
It's a pump dispensed one, with delay bleed tube for gradual oil delivery.
It then branches into two, one going to the inner side of the front sprocket. This gets the inside O-ring and also feeds oil under the central roller. This worked fine but I noticed that the outer O-ring looked much dryer so felt the need to add the additional feed tube.
The additional one is just a simple feed tube over the top of the outside O-ring as this will splash when it hits the chain thus lubing the outside Oring as well as providing a general all over coating to the chain.
I had to put a cable tie end in this pipe as well, even though it's not used, just to maintain the feed balance as without it all the oil was flowing down this tube and missing the first one.
I like making chain oilers btw, can you tell....