Watch the Bluegrass Banjo Technique online guitar lesson by Muriel Anderson from 50 Right-Hand Techniques You Must Know
Bluegrass banjo players brace two fingers of the right hand on the face of the banjo, which produces some tension in the sound. So to imitate the sound of a banjo, I tense up the fingers of my right hand, and play with a brighter sound down near the bridge.
In addition, it's important to use the thumb in the same places that a banjo player would use the thumb. That provides an automatic accent in the right places. This excerpt from "Foggy Mt Breakdown" is from the bluegrass medley, taught in its entirety on TrueFire's "Innovations for Acoustic Guitar " DVD.