Definately there is a way. Here at our studios we constructed a material based on Parallax Plaster Paint. The trick is in the Lerp. You need to apply a Lerp twice, one above the vertex color responsable for the plaster and one below, and both Lerps should be painted with the same vertex color. The mix map you are using to paint the plaster has a Fall Off. When you increse the fall off you will reveal the lower part revealing the AO. Now the AO is generated by multipying the previous vertex layer with 0. The result of this multiplication will be painted with the same vertex generating the parallax.