You don't say what your appliqué is so I don't know how helpful this will be. If it is flowers, for example, then you can simply put a couple of decorative stitches in their centre. For leaves you could stitch some 'leaf art' i.e. stitch some lines so it looks like veins on the leaf. For animals, fur, etc.
Alternatively, if the quilt is not going to washed a lot, you could stitch round the outline of the appliqué with invisible thread (it can go brittle if washed frequently). Good luck whatever you decide.