I assume Hummingbird is talking about chords. For the purposes of the 3 chord songs you can use a capo and never have to play a non "cowboy" chord. A song in e flat is the same as a d with the capo at the first fret. Of course you'll have to transpose e flat to d; a flat to g; b flat to a.

Bar chords are just a pain. I cheat (I don't play guitar very often) by using half bar chords a lot. You can play an f chord with the first finger only on the top strings but you lose the bass note.