[rules-users] CEP Question

Hi All, I am still working through a CEP use case which is going fairly well. I have a few rules and it seems they are working as I expect. Is there a way to get called back when events go out of a time window? My current use case is alerting, I have a stream of events (param updates) coming in and I create a ParamUpdateEvent for each. I have a rule which averages the values in the ParamUpdateEvent and tests against a threshold, that is working fine. The problem is when I don't receive any events for a period of time over the window size I really want to the rule which calculates the average to fire when anything is moved out of the window as well as when an update arrives, is this possible? Thanks Glenn