I love invisible thread. The new kinds are very thin- about the size of hair. My package of hobbs 80/20 says to quilt no more than 4" apart. I'm thinking with invisible thread that you could do a "star" in the center of each block- - like a big X corner to corner and then verticle and horizontal lines. That should cover enought blocks to keep it within the quilting guide lines. You may need to measure and make sure.