Currently RadTreeView does not support such scenario. The ExpandItemByPath functionality works by creating a path from the string representations of the Headers.
However, we find your idea extremely interesting and we will make sure to implement it as soon as possible. The earliest date for this feature will be the Service Pack release, yet I cannot guarantee it with 100%.
I have also updated your profile with 500 Telerik points. If you have additional questions or comments let us know.
the Telerik team