I get the vibe you are making this more complicated than it needs to be. I do understand your desire to have a clean look, we can help you with either over the top returns or through the back, heck even through the overflow. We just want to see you happy with it.
It can be intimidating to set up your first overflow, but once you get it figured out it really isn't bad. So you need to decide, will you be happy with over the top? Or do you want it through the back or overflow?
That is a fairly good link, however there are a couple problems that come up with a herbie having a trickle in the second pipe. One, the second pipe needs to be able to handle as much as or more water than the full siphon in case of a clog. If some of the water is going down the emergency line, the siphon isn't handling everything and may get backed up if it needs to go full siphon. Two, with a trickle of water going down the emergency line you run the risk of something getting into that line as well blocking it up.
I will say, these things tend to happen much more with reef and planted tanks, but it is something to consider. In the process of setting my tank up I had a couple times where the siphon was closed too much and the emergency kicked in. I was very glad to have it running to take all the extra water. Something to consider!
Hard to tell from the pics, but it looks like you have either 1.5" or 1.75" drains, I imagine 1.5". In either case, those will flow a boat load of water.
So it comes down to how do you want to do this? As I've mentioned, if you want the clean look, drill two holes, one on either side of the overflow and go that route with a bean style overflow. Or you can go up over the top if you dont want to drill. Either one would be pretty simple to accomplish.
Can we see some more pics of the tank? A full tank shot maybe? This tank seems amazing, I'd love something similar.
