I beat Fontaine in little over a minute. I beat him using just the Target Dummy plasmid and my wrench. I use these tonics: (as well as others, but they aren't worth mentioning)

Wrench Jockey 1+2, powers up my wrench
Wrench Lurker 1+2 critical damage with wrench when enemy isn't aware of me (when his attention is to the target dummy)
Sportboost 1+2, speeds up my movement and whacking speed
Bloodlust, it restores any lost health and eve by whacking my enemy will the wrench

I use the Target Dummy plasmid to direct all of his attention away from me while I whack away at him with my wrench.

I love this game, I can't wait for Bioshock 2!