WLM,
Unless they have changed recently R44s are fitted with lap and diagonal chest restraint belts. However, your point is well made that the degree of restraint is less than a full harness.
The R44 belt only has 3 hard points on the airframe per seat. This rather limits the options. I cannot imagine that Frank would be happy for you to go drilling holes in his design
I am a bit worried by the reliability of the inertia reel found in many restraints, but having them certainly makes it easier to stretch to far flung parts of the cabin.