I've had good success using either Detail Master's thin detail wire, or, spark plug wire, in whatever color chosen for a particular project. You can drill a starter hole in a seat corner and glue the end of the wire in the hole with CA glue (obviously after you have the seats either painted or flocked). Then apply a tiny drop of CA glue about every quarter inch around the edge of the seat (or wherever you want the piping) until you complete the piping, After all the CA glue has dried, if there are ant shiny spots where the CA glue is, you can brush on a spot of dullcoat to knock down the shine.