No flush mount cause of visibility as cman stated.
The only reason I didn't mock up one with a round spacer is because I couldn't find or think of any materials to make one out of. The only way I could figure to do so would be to grind of one of the couplers I got down to round and that would require me to go to a friends that has the tools for that. The biggest limiter for me was being able to find the hollow all thread in 3/8 16. If I could have found longer pieces of the hollow all thread I could have used a real spacer or something instead of a coupler. All thread rod is common everywhere but not the hollow stuff in the right size in picth is not. I know I could order it online but didn't really want to. Ended up just getting some 1" bolts and drilling holes down the center of them to fit the other end of the coupler and bolt it to the bike. A $4 drill bit for stainless and about 15 mins a bolt and it was done.
One limiting factor for me is a basic 240 mechanics tool set, a dremel, and 18v cordless drill pretty much make up my tool set. I don't have the skills or tools to do more complicated peices. For the bolts I drilled them with my cordless drill and held the bolts with a pair of pliyers. Not the best setup but I made it work. It would work great if I had a drill press. A 2 or 3" bolt with a hole down the middle with a spacer and I would be set for a round stem,