I've tapered down my benzo use before (and am currently doing it again) by taking just a little less each day. For example, a week ago I was on 30 mg temazepam for sleep. Then I cut that down to 29 mg, then 28 mg the next night ... last night was 23 mg, no significant w/d so far. I'll post a guide on how to precisely take these kinds of fractions of pills in the future, but right now I need to work out some problems inherent to the method. It can be done, however.
As for the lorazepam: If it's being administered IV, obviously it's in liquid form and has to be in a syringe at some point. If graduated 1 cc syringes are being used, inject, for example, the normal dose - 1 mark, then the next day the starting dose - 2 marks, and so on. Obviously, you'll have to adjust that increment depending on how many marks are on the syringe (I've seen 1 cc syringes graduated in 10 uL and 20 uL increments), the actual volume of the dose, and how you handle the w/d. If the dose is > 1cc, see if you can switch to multiple shots from a 1 cc syringe, as these have many more marks (and thus more control over the dose) than larger syringes. I've never come across a smaller syringe, but they might be worth looking into.
From experience, I'd say that you can take off about 3% from the starting dose per day, but of course everyone is different, and with benzos especially this linear taper breaks down as you approach zero.