empty field

I've been stuck on this issue all day now. Is there a way to pre-populate an 'empty' field of any type with data?

I've tried Rules, specifically 'Set a data value' but it does not appear to allow data values to be set on empty fields and usually reports back (in 'Recent Log Messages') 'The variable or parameter entity is empty'.

The reason I need this is that I have a 'profile type' (using Profile2) with various fields. These fields are updated - when required - using VBO (Views Bulk Operations) and unfortunately they can only be updated by VBO if the fields have existing content.

I am trying to write a rule to match an empty field and am not having much luck. I've tried about everything I can think of, including some very inventive regexes, but no luck yet. Anyone know how to accomplish this?