Can you give me a little more information? How big is your cat? Was the lorazepam prescribed for him? What size lorazepam do you have?
I would try giving your cat 1/4 of your 0.5 mg pill and see how he does on that. If not sedate enough, you could give another 1/4.
I disagree with your vet about the rabies vaccine--you never know when a bat or rabid animal could slip in. Not to mention that, at least around here, it is a law that requires it. But no matter, you didn't ask my opinion about that!