'88 trooper fails then passes the drive clean 2X(NOx help!!)

In Ontario you have to pass Drive Clean to renew your plates. Mine (for the last three times) fails the test (for excess NOx) then I scramble around, try a few things and somehow cajol the technician to complete the test when the exhaust is really warmed up. My brother thinks I have a lazy catelytic converter.
I can't take the stress of scrambling each time.
What can I do (short of replacing the Cat - which I will if I have to), to reduce NOx and pass the first time?
I am due for valve adjustment, I am due for an oil change and I run regular gas.
Ideas?