Personally, I've just spent myself out of that problem - I bought a German Kern-Stabi adapter plate. The ****ed thing cost a fortune, but it was the quickest and easiest way to get a superb lift adapter so I grinned and bore it.
It also hooks into those exakt frame holes, and I haven't seen any info anywhere that the R3 Roadster is any different to any other Rocket. The one thing to keep in mind is that newer Rockets have 9mm holes there, the older ones were 13mm or some such.