Last autocross I used same seatbelt trick, but I had to get seatbelt to stop like a inch or 2 away from buckle then force it in or it would come loose, was actually decently effective but hurt my chest, lol. Still didn't hold me as well as harness. Before I used simpson 5 point (which I will be using again) and it was great. I just got one that had long straps in the back and bolted them to rear seat belt bolts, and it helped out a bunch.
2002 svt focus 168whp 153wtq
1993 Honda Civic (For Sale)