Treegrid with extra filterparams to server on node expand

I have treegrid that I want to send some extra filterparams to the server on each node-expand.

There is 1-3 extra filter parameters that I want to send to the server besides the the node-id.

I´ve tried the beforeload-event on my treegrid to see if I could setParams on the operation object but it won´t fire!?

Treegrid with extra filterparams to server on node expand