Thanks so much for your concise direction!
Now that I know what I'm looking for, I found it, kind of buried, in the online manual. I must not have used the right AI queries when searching this issue out.
However, for those of us familiar with using two EXP1 pedals on a Helix Floor, this is how the HF interfaced with EXP pedals - two plugs, two cables, two pedals, learn controllers - done. I'd recommend a change of default for C/D because others will be trying to apply the same, learned process to implement two EXP controllers.