BlenderPilot, with 50 gal you're flying about 1.5 hrs I guess; is there an option to have a stock of, say, 25 litre fuel drums on the way, drop in for a quick hot refuel during the job (10 minutes time out, and a bit of logistical work to put the drums there) - take off lighter in the first place. The answer is money, I suppose.
With the conditions you're working in, sounds like the Jet Ranger isn't the right machine for the job considering you have to flog it to do anything much.
I know there are probably numerous reasons why the situation is as it is, and from what you say you are getting away without harming the engines; still, why would they bother putting a 5-minute limit there at all if they meant for us to pull to it for way longer than that in,say, an hour. Part of the problem is that the limit is too wishy-washy, of course - if they were more specific, there wouldn't be the option to dodge the issue.