Being a clawhammer player in England - most sessions you find tend to be mainly Irish music, so I used to be limited to vamping along with chords. This quickly becomed boring. When an Irish session started in the village, 5 minutes walk up the street, I went along and after a while started experimenting. First I used clawhammer techniques to create rhythmic patterns within the chord shapes I was using to back up reels and jigs. Some of these proved to be very effective, filling in the spaces around the melody. Later I started to develop my own style of playing to get as much melody line as I could reasonably fit in. Some tunes can be played, but others are nigh on impossible - it mainly depends on the direction of runs or arpeggios.
With jigs, I found that I mostly ignored the fifth string, instead using a lot of drop thumb onto the other strings. As many of the tunes are in D or even A, I had to work on ways of playing in those keys without needing to retune from standard open G. Forming a barre over strings 1,2 and 3 at the second fret leaves the D and f# of the fourth string accessible for lower runs. I could then split each bar into a group of three notes playing in a pattern I H I, I H I. with the tiniest virtual pause between the two triplets. The odd full chord thrown in at appropriate moments can also be effective for emphasis.
When playing with others, they will be mostly playing the melody line, so it isn't always necessary for the banjo to be simply echoing them. Try counter melodies based around the back up chords. Intersperse melody line, when it is playable, with chords and rhythm when the melody falls into a pattern incompatible with the physical restraints of clawhammer. Most important - HAVE FUN!
Quack! Geoff the Duck!