Sorry for the delay!
I had a look and now i can answer for sure!
I did't use any special bolts. I did use my original bolts. They work just fine almost 2 years without a problem.
And, yes, there is a small lip at the edge of the spacer so the rotor can be cendered.
The small lip explains why i didn't use longer bolts to center the rotors.
The rotors stays centered by the lip of the spacer and the original bolts keeps the rotor tight on the wheel.
As far as i remember i've paid 120 euros for my spacers (almost 200 USD back then) and it was a friendly price!