I would stitch a darning type stitch to keep the slit from spreading, then I would cover it with an applique. To make it seem intentional, I would scatter a handful of applique motifs over the back, possibly working in some of the information that would be on a quilt label -- name, date, recipient, occasion. Make your applique shape tie in with either the pattern on the front or some motif from the fabrics -- ideas could be a simple leaf, hearts, geometrics, flowers, butterflies -- all depends on the style of the quilt.
RST