Yeah I've tried it. It seems to work better to put the additional friction above the hitch. That's why the ZK-1 Rope Wrench is located above the hitch. Works very well.
If your added friction is below the hitch, the hitch tends to grab hard before the lower friction point can have an effect. The rope wrench takes approx. 50% of the load off above the hitch and redirects it through the wrench tether to the climber's attachment point below the hitch. That's what allows the hitch to function like it's in a doubled rope configuration, the hitch only works well when it's holding approx. 50% of the climber's weight.
A climber could theoretically take that 50% load off below the hitch but it would be very unstable, very difficult for the climber to maintain that balance on descent, so there would be lots of stops and starts.
One thing you might try low and slow is to simply run the rope through your feet with the same rope path through your feet that is used in footlock technique ascending. I've done this, you open your feet up more to descend, close the feet in on the rope path to go slower or stop. You'd have one hand on the hitch and another just below the hitch to push it up and lock to stop movement. In this configuration the hitch has no adjustability, it's either wide open or locked, your foot positions on the rope are the control. Very sketchy, requires significant practice low and slow to even attempt technical facility. I'm mentioning it to clarify what happens when friction is above or below the hitch.
Using a hitch with a figure 8 rappelling device below it is essentially an autoblock system, it works. A figure 8 will hockle or twist your rope significantly, can be a significant inconvenience.
ZK-1 Rope Wrench is quite inexpensive and light compared to any mechanical multicender or dedicated SRT ascent and/or descent devices that passes the "whistle test". That is, if I blow a whistle at a random time while you are on rope SRT, you let go of the rope with your hands. If you free fall your system does not pass
You can easily imagine a number of circumstances in SRT tree climbing where you can either be forced to take your hands off the rope or accidentally take your hands off the rope at the wrong time.
-AJ