As you know, I installed the factory diverter valve but before then, I also considered going the route you proposed. Obviously, the cost will be more than $100 as you are going to have hoses made, brackets to fabricate or purchased, and other incidental expenses. Before I went the factory route, I surmised that it should indeed work and in reality, it shouldn't matter too much that you are operating/controlling one at a time. For me, I thought of installing that valve onto the factory diverter valve/power beyond bracket so that I could install quick disconnect couplers at the factory location so that the top/tilt cylinder hoses are not stretching where they weren't designed to but that bracket is almost $100 by itself. Then I thought that I would install (2) of the manual selectors so that I could install two new rear remotes and keep the third rear remote but then it started getting complicated and the cost kept going up when I calculated all the stuff I wanted to do and itemized all the parts. Then I thought about the physical size of those valves and how/where I was going to install them and got a headache, especially when trying to balance ergonomics and aesthestics. Finally, I am not a huge fan of lots of flexible hoses so I decided to go the factory route.
If you do get the manual selector valve plumbed into your system, please post how you did it and your experience with it.