As already mentioned, it's not possible to set the state directly to Intermediate since this state is calculated dynamically.
The client-side event
that you need is OnClientNodePopulated
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.