Wrapping the belts around a bar is always better as it takes out a short radius bend in the belts and distributes the load better. Of course this is contingent on having an appropriate bar. As previously mentioned it is much better to attach the belts just behind the seat as this limits the amount of stretch. The angle is also very important, and not just for HANS applications as mentioned as compression of the spine is a big problem. I understand that a competitor at last years Alpine Rally hit a tree and the belt compressed his spine resulting in some spinal damage. The CAMS manual is the best source of information on this.
 
The bar shown above mounted in the boot is a good compromise for cars without a proper roll cage. However don't pass the belts over the back seat as this will deform in a shunt and effectively lengthen the belts. Using approved belt/seat plates in the same location will also work and will be much lighter.
 
All good harness manufacturers supply with eye bolts but can be removed for a wrap application.
 
Hope this helps.
 
Cheers, David Vervaart. VSport Victoria.