Yes, caffeine is a great vasoconstrictor.
My clusters also last about 8 weeks. (Almost every year or so for 25 years.) But I don't know what a mild CH feels like -- I'd rather "check out" than face a full-blown cluster without oxygen.
I've been able to skip a couple years by doing the following: at the first indication of a shadow, completely cease both alcohol & exercise, and start taking 100 mg of caffeine every four hours.