Hey, I have almost the same problem.(Except I am scripting the summoning behavior on my own)My guess would be create new Status like Soul Bound(SUMMONING_ABILITY in the stats) and script it's behavior. The problem is I have no idea where it's defined. In Docs there is nothing about linking the Owner with it's summon and how to define such a behavior.
Tl:DR it seems to be hard coded :(