Need advice on transplanting peonies now

I know that fall is the best time to move them, but we’re moving now so I don’t really have much of a choice and this peony belonged to my great grandmother so I’d like to take it.

Since it is the wrong time of year, is there anything I can do to increase its chances of survival?

Can you insert a clause in your contract of sale that the peonies are yours and you will transplant them in Fall 2018? 

Here’s info from web:

If you must move them in springor summer, dig the plants carefully, disturbing the large root ball as little as possible (dig a deep, wide hole to ensure this). Then plant the peonies as soon as you can, taking care to plant them no deeper than they were growing before.

They will probably be fine but peonies don't like being moved under most circumstances so it could take a few years before you see blooms again. Don't despair; they just need to settle in.