Thread Focusrite Control configuration question

Hello,
I’m a newbie to this forum as well as my recently purchased Scarlett 18i20G2 and the Focusrite Control app. I’m a keyboard player who is just venturing into using my MacBook Pro onstage and am using the 18i20 not only as my interface, but also as a line mixer. My current onstage snapshot has two keyboards going into inputs 3/4 and 5/6, which are stereo linked. I’m using Gig Performer as my host app and have a preset that consists of an audio file player playing stereo tracks, one side being a click for the drummer and the other track outputting whatever audio track is recorded to FOH.
I am routing those DAW tracks to outputs 3 and 4, which go to FOH where they are routed appropriately. Keyboard inputs 3,4,5, and 6 are routed to outputs 1 and 2 which I set and leave the level with the monitor out knob which then goes to FOH.
Since I usually have some onstage amplification to monitor my keyboards, I’ve routed inputs 3,4,5,& 6 to outputs 7/8 which then go to my onstage amplification.
Here’s where I’m confused - I need to have separate level control for my stage level. I was hoping that since those outputs are also sent to the headphone outputs, I could use the hardware volume controls on the 18i20 to adjust the level on the fly if needed, but realized that this isn’t true. I’ve been adjusting their level inside the Control app Besides connecting a stereo splitter cable to one of the headphone outs, the right and left signals to my amp, is there any routing configuration I could set up in Focusrite Control fo allow use of the physical headphone volume knobs?
Thx!
Mark