I fitted bonnet mounted driving lamps to the R50 Mini Cooper I had about 10 years ago. I used the following wiring arrangement:
The main beam supply to one of the headlamps was tapped off and routed to drive the coil of a normally-open relay.
One side of the relay contacts was routed to the battery positive, via an in-line fuse (think I used 20A).
The other side of the relay contacts was routed to the additional lamps.
This method worked well and no bus errors appeared, albeit on a 2004 car. Don't see why it shouldn't work on a 500 though.
Have you sourced lamps and mounting brackets? Lots of aftermarket stuff was available for the Mini, not so much around for the 500.
Remember there are lighting regs for the positioning of driving lamps.