I played in a show with a string section recently. The sound guy made these pckups for the strings out of really cheap parts from radio shack and they sounded better than the ones that cost hundreds of dollars that some of the players had. All he did was carefully break open these puppies:
http://www.radioshack.com/sm-piezo-e...i-2062402.html
and solder quarter inch connectors to them. you could use double sided tape to mount them on any acoustic instrument but he used post-it putty because it helped attenuate some of the harsh frequencies these can produce.
Over-all they worked really well and would work on any acoustic instrument.
Time to get crackin'