One thought - since there are a couple ways to do stained glass quilts - how about using a black fabric for the base? If you are using black for your "leading" color, any mistakes, odd fits, and such would visually blend in and be perceived as lead.
I have only done small stuff with stained glass techniques, but they are fun and look great. I used a double needle and black thread to secure the tape and pieces butted under it.
I made my pattern by transferring my photo to Paint Shop Pro and increasing edges, then reducing the colors until I had something workable.