Hi,
The engine modes themselves all happen on the client-side, and they basically determine what ends up in the processing queue.
I think the solution you may be after here can be achieved using the
Test filter configuration setting. You can define a custom filter that applies to your local machine (as this is global affecting all engine modes) that will stop it from executing the long running tests. Assuming this filter isn't assigned to the grid node, the node should be free to pick up these tests.
Or is the issue that you want this behaviour to be easily adjustable? (i.e. at the flick of a switch).
Cheers,
Remco