It seems Arturia have copied the way the Matrix 12 works all the way,
Although Pedal 1 is normally Volume and Pedal 2 is sustain on the Oberheim, where as Arturia seem to have gone the other way.
So, if you route the PEDAL 1 to ENV 1 RELEASE, and PEDAL 1 to ENV 2 RELEASE, and set the amount to MAX on both, that will give you the conventional "Hold Pedal" function.
Note that you may need to do the same for ENV 3,4 & 5 if used in a sound. (You can get some interesting "half" sustain effects using lower values)
This was also how the Matrix 12 worked for MIDI Volume as well, you had to route a PEDAL to VCA 1, though fortunately, Arturia have allowed the Matrix 12V to always receive CC7.
Note that this is Patch specific, so you have to do this for every Patch,
but this is totally faithful to how the Matrix 12 worked.
I cannot find anyway of changing the CC allocation to the pedals, PEDAL 1 is CC64 and PEDAL 2 is CC11 - they seem to be fixed.