war of the worlds and the dilemma of grease

Bear with me on this...

I've got a set of Ronal R8s from an Audi 200 Quattro, ET45, the centre bore of which I've had machined out to clear the front grease caps... but not right through, so that the wheels' original centre caps will also fit.

So far, so good. However, having had a closer look at the grease caps today and after some time wielding my tape measure, it's obvious that I've got a problem. In order for the hub grease caps to fit under the lip of the wheel's centre hole (so that the centre cap will still fit) the distance from wheel/hub interface to the end of the grease cap must be 40mm or less. Currently the distance from hub flange to end of grease cap is 60mm. So that'd mean a spacer of 20mm, which would reduce the effective ET to 25... which is a bad thing, right?

Originally I thought that I could reduce the depth of the grease caps a bit, but they're 35mm from lip to end and I really can't see any way of reducing that dimension by more than a millimetre or so, which hardly seems worth the effort.

So I seem to have two options: screw up the ET of the front wheels, or have the centres bored out completely, forget the idea of running the original centre caps and live with the grease caps poking out through the middle of the wheel.

Opinions? Advice? All suggestions gratefully received!