I've always found it irksome, the rule that you oughtn't butt cloth against cloth in bookbinding. Paper/cloth and paper/paper are fine, but that fraying bare edge of unfinished cloth will not do. When I became set on a quarter binding in two shades of silk for my recent collection of eco prints, I appropriated a embroidery technique to join the book cloth.
For this cover I've sewn a herringbone stitch (a quadruple herringbone if you will) to create a woven net joining the silk. The herringbone stitch is the foundation of many stitches including the interlacing stitch, which has a long history of use in Europe with many variations, both on fabric and across seams. Any number of stitches could be used for this bookbinding purpose, following the diagram I've drawn up below. Some useful interlacing tutorials can be found here and here.