Hello Michael Hassinger,
You could take advantage of the property e.Options.Source which keep track of the source element being dragged (in your case this could be ListBoxItem) and then check which listbox it belongs to. Let me know if you have any questions regarding this scenario.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items