There is a fire both selection in the mapping, but no there is not a setting availible as you described. The practical reason for this may be that your secondary wepon may be a bomb, torpedo, or rocket in some planes. This is how I have the top buttons set on my cyborg3d:
Trigger: Fire primary
Button 2:Fire secondary
Button 3:Toggle stick set (toggles views)
Button 4:Select secondary wepon