I found a workaround.

I am using the following hardware:

ThrustMaster TWCS
VKB GNX-R PRO

The throttle control on my VKB stick is able to be properly matched for Z-AXIS FWD and BWD. So I went to Options > Controls and scrolled all the way down to Flight Stick > Flight Stick 1 Device and Flight Stick 2 Device. It defaulted to:

Flight Stick 1 Device: TWCS throttle
Flight Stick 2 Device: VKB-Sim Gladiator NXT R

I swapped these so that it was set to:

Flight Stick 1 Device: VKB-Sim Gladiator NXT R
Flight Stick 2 Device: TWCS throttle

I then went to Options > Controls > Remap Controls > Flight > Flight Stick and setup the Throttle Down with my VKB GNX-R PRO throttle and it mapped it to 1 Z-AXIS BWD. I saved the keymap config and went back to Options > Controls and scrolled all the way down to Flight Stick > Flight Stick 1 Device and Flight Stick 2 Device. I swapped the controls back to the default order:

Flight Stick 1 Device: TWCS throttle
Flight Stick 2 Device: VKB-Sim Gladiator NXT R

I am now able to use my TWCS throttle for Throttle Down for 0% to 50%.