One option is to ask the volunteers to furnish all the desired information in the one textbox, but that there is no submission validation.
I also would be interested to pay for an add-on that would permit more custom fields, but my organization can’t solely support the level of programming described by Mr. Sherrard. In our case, our current need is for a form with a required ‘Y/N’ radio button, but it would be OK to have another text field. We are just asking in the submission for the user to provide both pieces of information in the one box.