I was also wondering if there was a converter for this, not that I need it, but it would be nice to have.
Is the DiscEX source available ? You could probably try to reverse what DiscEx does to the .iso when you convert it.
Isn't all that DiscEx does is take what is inside the .iso and place it in a folder ? If so, it might not actually be that hard to write a tool to reverse
it. I can't even find a freeware ISO editor to even see if this is true though.