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The problem with adding to the WFD form, is where are you going to store the data? It integrates with Formulize right out of the box, no need for any hacking or updates or patches.
You simply need to make the form in Formulize, give view/add/update permissions in Formulize for that form, to the groups of users who should be able to see it (Registered users probably). And then in WFD, modify the category you want to use that form with, and pick the form. I believe that's all there is to it, though I haven't done it for a little while.
--Julian
