regalpierot

Ha. I initially saw your post, and much as I appreciated the response I knew I had an unassigned switch spare (happened to be the FS2). But it did make me think a little more in that regard and thought I'd try to make footswttch 3 (where the looper is in the factory presets) the free one. Presto, I was suddenly able to add a new looper. Be interested if anyone else has a HXFX to see if they notice the same thing.
 
Thanks so much Phil, you got me looking in the right direction mate.

@highline, I'm pretty sure @HonestOpinion was giving you a suggestion not a misunderstanding of what you were asking. 
 
Cannot be done at present. The Helix Rack is the only product in the family that has a dedicate Exp input that can interpret pedals with that function (and most likely you'd want the Mission Line 6 pedal made with that additional feature, think it's about $10 more than the one without). May be in a firmware release down the road, but I somewhat doubt it. For now your choice is
 
1 - Dedicating a button to Engage\Disengage for the Wah etc (my current choice of workflow). 
2 - The auto-engage at a point (can be heel down or a custom position of your choice) which is tricky if you keep hitting that spot during playing and haven't the timing set right
3 - A conventional wah in the chain
 
That's about it.