Preferred Name fields

Hi all, we're looking at some preferred name issues:

We will not be allowing a preferred first name without a preferred last name -- previoulsy, if someone gave a preferred first name only, we would append their legal last name to make a complete preferred name. We are planning on adding 3 name fields (f,m,l) to supplemental questions. We could make them all required (or at least first and last). Or we could leave them optional, but have a note that if you enter a first you must enter a last also. Ideally, it would be nice if we could require last only if first is entered -- perhaps make the section optional, but the fields required, but I don't think that would work the way it's desired.

Has anyone else had a similar need and/or solution?