This is a fair concern, so let me clarify: I usually hike out of camp and once I am far away from where anyone would ever pitch a tent or even set a chair, I use my boot to scuff out a spot of bare ground or sand. If the spot I cleared is free of twigs or rocks or vegetation, it's very easy to make sure I don't leave even a tiny speck of poo on the ground.
And if I suspect I might have a wet poo on the way, I simply put down a couple sheets of Kleenex or paper towels first and that acts to absorb any extra moisture. But usually that's not necessary.
Finally, after picking up all waste (including TP) in a dog poo bag, I scuff some loose sand or forest duff back over the cleared spot.
I can't speak for other self-support kayakers, but I am confident that what I do is just as sanitary and LNT as anyone using a traditional groover.