Custom Output Element/View help

Does anyone have any experience constructing a view to hold a single row per customer that constructs the email value conditionally?  What I'd like to do is have the view provide a specific type of email for the customer but, if that email type does not exist, to then provide the primary email address.  Basically, I want it to function just like the email parameters for executing an output set, only I can't use the "execute an output set" utility because I need to be able to select the output set in WordFly and get only one email address per customer, using only one list and output set.

Sorry if this is hard to understand. I am hoping against hope that someone's response is going to be "why would you do that, you should just do *this thing* instead."