Well, I'll assuming you are playing in 4/4...
Use the technique open-hammer-pluck and play the following arpeggios
E-E-A-A-E-E-D-D-E-E-A-A-E-A-G-E
Basically, for the E arpeggio, which is pretty much a E power chord, but anyway... hit your open A string, hammer on 7th fret on the A string, pluck open G string, hit your open D string, hammer on 9th fret on the D string, and pluck the 9th fret on your G string... Same goes for A except you shift up a few frets... etc, etc. It should sound something like a banjo roll.
Here's a clip of something I played a long time ago, using that technique. (the beginning's just crap, what I talked about comes in at 0:09)
http://www.youtube.com/watch?v=dyE503mUncw