@phil_m
No - one of the blocks in question is bypassed, but the other will be on in every snapshot, with just the ability to adjust the parameters with EXP1 in a single snapshot. So it would work in one direction, but not the other. If I had one more block, I could do it this way, but as it stands, I've optimized everything as much as I possibly can. Instead of getting a second expression pedal in the short term, I will just do volume swells with my guitar knob - I always used a pedal for this, but I've gotten used to using the guitar volume pretty much now. Longer term, I'm looking at a Boss OD-200 to free up the two drive blocks and the noise gate block I'm using. That will allow me to use the method you are proposing for sure. The OD-200 is programmable and midi controllable by the Helix. It would be placed in the loop I am using right now for a Tech 21 SansAmp (my "amp" tone - clean/edge of breakup), so I would not need to use a block for another loop. It also has some key models the Helix family is still missing (Blue Driver, for example).
The idea is to minimize the outboard pedals on my board and use the HX Effects to it's full ability. Just the HX Effects, SansAmp and 1 expression pedal would have been great, but unless they give us another block or two in the HX Effects, it's not going to happen. One thing that would be nice is if the input block, which is fixed with no adjustable parameters in the HX Effects, had a rudimentary noise gate like the Helix Floor does. That would free up the 1 block I'm looking for!