Originally Posted by waterrockets

Yep, it's actually really easy to make minor cable adjustments to the front der w/out a barrel. Just put it in the big ring, then shift to the small ring without pedaling. The derailleur will hang on the chain, and the cable will go slack. Make your adjustment with the slack cable, and try again.

The barrel is easier, but you still can't do it by sight -- it's going to be trial and error, so the barrel really isn't needed.