I once took a Machine Trapunto class and they used the wash away thread to quilt the design first; then cut away the excess batting beyond the design; relayered with another entire piece of batting; then sewed the design again with regular thread to complete their work with all the design details. It works very well! I tried it in "plain" setting blocks on my dsm, then set those in with the pieced blocks, finally layered the whole quilt and quilted as usual. You can find more information from artists like Karen McTavish, a gifted Longarm artist, or Hari Walner that does quilt designs.