Hi Steve! Interesting question but well over my abilities! I did find this old post where someone talked about grafting itohs, several replies down. Good luck with your experiments!

Here is a link that might be useful: grafting peonies discussion

In September I downloaded an incredibly detailed description of peony grafting(39)pages. crickethillgarden.wordpress.com Al

I did it already anyways so even if they don't take, the itohs shouldn't be harmed much anyways. I don't see any reason why it wouldn't work since itoh peonies are closer to herbaceous peonies anyways.

After a few days of healing, it does look like the buds are still very firm so I think they are taking. I also grafted some itoh buds with a bit of cambium material on, right onto some itoh peony roots of the same plant so I hope that works well too.