I don't think there's a way to do this using the Management API. You can use the SourceCode.Workflow.Client API:

WorklistItem oi = K2Conn.OpenWorklistItem("24_9");

oi.Sleep(false); 

If you need to do this using a user that's not the actual destination user, you may need to call the Impersonate method before the Sleep. Note, I have only tested this in 4.5.

Thanks a ton, the code works