I've been thinking about the same thing now that I'm sure 'Regal Splendor' will stay where it is. (This is the first year it has bloomed since I moved it two years ago).
My thought today was that I would put a couple of small blue hostas which I have - 'Halcyon' and 'Full Moon' at the base of RS. I just received a division of 'Ripple Effect' as a bonus plant and that might look nice between the blue ones. I think 'Cameo' will stay quite a bit smaller and I prefer to keep the 'Baby Bunting' family all together.
Ann