The habit of the tree is distinctive enough that it deserves to be a stand-alone specimen. Plus, you will need that space for the 'skirts' to spread. Best if you just use a groundcover in the area....something like Veronica peduncularis 'Georgia Blue'.

Whatever you choose, you do not want to plant anything that may need to be divided regularly or require frequent replacement (like annuals). JM's have a very delicate and sensitive root system that resents any disturbance.