Alert on Specific "No Data" Duration

I have added a few strategic alert rules for datapoints (like WinSystemUptime/SystemUpTime that generate alerts for no data (in this example, to be aware when WMI wedges).  However, there really is no method to indicate how long that should be true before turning into an alert other than the consecutive faults count, which is not really ideal to use for both normal and no data cases.  I can hack this with empty escalation chain stages, but it would be nice if these alerts have a time-to-trigger value distinct from regular alerts.