Being out even with fixed reserve of say 30 minutes is an issue. Survival gear can be played with a bit or a pet rock under the rear seat with pax and at front of cab without pax. If you are somewhere that you can't pick up water or sand or it's rather strange to the pax for you to be loading sand etc after drop off with only say half hour out of full.
Very good to see you worried about it, I suggest you spend some time talking with the A&P weight specialist and senior pilot on the job and do quite a few sums, it seems a bit far back to me.
I always set up these and the KH4's with CofG right at rear margin with full fuel and reasonably light pilot, making sure they all knew how much ballast to carry and where, cos when that fuel gets low with a full cab and the cyclic is right aft you need to make sure you have enough to flare if need be.
You could always carry a few pet rocks out to each fixed location for use when required.
As AC says keep it legal having someone jump all over yer head is an ugly scene, in this country at least.