I'm familiar with that controller, but never purchased it. I can only offer some generalities from my own controller setup with the PitchFactor. I'm hoping that may help you to work out the specifics.
You'll want to emulate the momentary action of the Eventide switches using MIDI CC messages. It sounds like you're very close, so there's no need to go into matching MIDI Channels, MIDI CC numbers, system settings, etc. For whatever CC number that you've selected in each device, there'll also be a CC value sent. It will also has a valid range of 0-127.
A CC value of 0-63 is considered "off", while 64-127 is "on". Most times it's safe to call 0=OFF, and 127=ON. From your description, it appears that you're getting an ON with one foot-press, then an OFF with the second foot-press. What you want to do is to emulate what a MIDI keyboard does: Push down a key for ON, then it sends OFF when you release the key.
For the SoftStep, you'd want a Foot On (or equivalent) to send a CC value of 127, with a Foot Off sending a CC value of 0. A brute force approach might have two Modulation lines set up like that – to the same CC number – without any other modifiers and variables in those lines. There may very well be a more elegant method (using toggles and such) that can be set up in a single Modulation line.
I'm working from the SoftStep manual here, with no real way to check it or provide an exact recipe. I hope this gets you pointed in the right direction.
