I probably don't understand what you want, but I would just hardcode the field names in my application (e.g. in a text box?)...
What are you doing with the two databases? Load in all fields from both, I assume. Do you force concatenation?
Otherwise you get a synthetic key table, do you?
Or do you limit the read in columns to the common set and want to show the excluded fields (see above --> hardcoded text). What is the reason behind to explicitely show the excluded fields?
You see, I am pretty unsure what you want to achieve, maybe you could add some more info.