Yeah the lap belt does ride up and its a pain, though once the racing seats are in, this wont happen as the belts come through the holes in the sides of the seats which hold the belts down. As for the CG Lock; I still have mine and it works well, not as well as a harness but to be honest, the CG Lock is pretty remarkable for what it is.
I'm not really buying into the arguement that says if harnessess are safer than standard belts in a road car, then all cars would be fitted with them on all seats. I'm sure car manufacturers would not want to pass that expense onto the consumer as this sort of safety measure would be deemed as excessive. Standard belts appease safety standards and laws, therefore, why go all those extra miles for something that is OTT?
When I'm belted in, I'm secured tightly to the seat. As I said though, its easy enough to give some slack when required and I almost never drive with the belts on with full tension. I will have a look at securing the belts in the seatbelt thing as suggested, that is, if I can work out how to get into those bolts.