I think your answer may lie in this Osprey book:
link
The Table of Contents indicates that there is a complete list at the end of the book with all such aces you are looking for.
The author is well known in the WWI aviation world and has written quite a bit for the well respected Cross & Cockade magazine of WWI aviation history. His bio on the Osprey site indicates he has published 11 books with them.
I do recall looking for this info a while back and it was extremely hard to find. Maybe my google-fu failed me but for WWI observers there was very, very little out there.
On the other hand for WWII, there is plenty of data. There was something along the lines of 350 American crew in bombers who reached ace status.
However, multiple sources indicated that these numbers are exaggerated and almost unprovable. It was almost impossible to tell who shot down a plane in a large bomber formation of hundreds of planes. Often times any gunner firing at the plane who saw it go down claimed credit. Some missions there were a dozen claims all for the same plane.
There was also a dash of wartime propaganda going on that did not want to look into the validity of claims. The more downed planes reported, the better.
There were no gun cameras that I am aware of commonly placed on WWII bombers, so proof is all done by various witnesses (often times from the same bomber) both air and ground.
Finally, I go to actual participants and witnesses who flew in the Army Air Corps as it was called at the time. I was fortunate enough to have several relatives who were AAC veterans of WWII that gave me eyewitness accounts. They all said 1) it was hard to even hit a fighter let alone shoot it down, and 2) if a plane went down almost any surviving nearby plane claimed credit.
I did have an uncle who was a tail gunner and shot down an Italian fighter. He didn't learn that he shot the plane down until after the war. He said he just saw a tiny dot in the distance, squeezed off a burst, and the dot dropped off. Nobody in their flight reported a kill. It was someone on the ground watching the bombers that reported it.
Factoring all that in, a logical conclusion is even in WWII with improved gun platforms and firepower for bomber gunners, it was still pretty damn hard for one gunner to shoot one plane down let alone five.
Now imagine an observer in WWI getting five kills.