I don't know if this is still vacant but maybe just a few thoughts how this is working quite nicely at my end.
If you're using a computer a very useful tool is the TransMIDIfier - probably well known here - there you can define Inputs and Outputs and turn your computer into a powerful MIDI hub. That is the way how I was able to use Line6 FBV Express MKII to control the HX Stomp.
You can set is up as follows utilizing its own software:
Volume = CC80
Switch to Wah = CC11 Toggle between 0/127 tu turn on Wah block or control the volume.
Wah = CC16
Preset Down/Up = Program Changes on a regular MIDI Channel 1
Bypass = CC70 Toggle between 0/127
All of this works i.e. also perfectly same way with the Source Audio Sloleman which has traditional MIDI connectors. You can also connet extensions, expression pedals and so on to it, it's great tool for MIDI!
Now getting MIDI to HX Stomp is a different story but here at least one option.
The BT/MIDI connector WIDIMaster is able to connect to any other BTLE/MIDI device without having a computer in between (i.e. with TransMIDIfier), but here I prefer a solution without having my laptop on stage.
So grab yourself at least one WIDIMaster and a second BT/MIDI receiver which can be anything, I'm using a Yamaha MD-BT101 here. So connect the WIDIMaster with the other one utilizing the WIDI tool on an iPad or your iPhone and you're good to go, no strings attached, the Soleman connected to the HX Stomp via Bluetooth over the air (WIDIMaster+Yamaha MD-BT101).