If I understand your question correctly there's a simple solution to this. Insert a wah block and a volume pedal block into your patch. Set them both to be toggled on and off by assigning them to the exp pedal foot switch, and make sure that the volume pedals volume parameter is controlled by the EX-1 pedal. Then insert a delay block and assign the mix parameter to be controlled by the EX-2 pedal.

Now EX-1 works as a volume pedal and when you press (hard) with your foot you toggle the volume pedal off (while still at its max value) and kick in your wah to be controlled by the same pedal. And the delay mix is by itself on the EX-2 pedal. I just gave it a try on my HD-500 and it worked fine.

Good luck!