Maybe some Bomba rhythms will work. Bomba drums have a wide range of tones from high pitched like djembes to lower tones like congas.
Tutorial on Bomba rhythms :
http://www.youtube.com/watch?v=Gf7hw8oG7ckBomba in Puerto Rico video :
http://www.youtube.com/watch?v=J09tYXHH0ukEncourage the other drums to learn some traditional rhythm, if they are not too intimidated by it. Why not try some stick rhythms using junior congas - less expensive and more easily transportable, and technique is less of a factor in the quality of sound? Why does a drum circle have to be all improvisation. Facilitation is often done at organized circles, which kind of contradicts the whole popularized notion of them. I participate in some of them, mainly for the friendships that have developed from my early years of playing, but I feel cheated at times, because they have me to enhance their drumming experience, and I have very few people to help me enhance mine. My philosophy has always been, what is more facilitating than an actual rhythm?