It just seems like reading the side cars LR3 makes would be an easy thing to do.
Indeed it should be easy. Maybe ask if someone in the PhaseOne community has figured out how to script it?
The other possibility would be to go through Expression Media (you should have received a free licence number for it). This will certainly read ratings from sidecars, but it can also write them directly inside raw files, which C1 could then read. A few caveats though - not sure you'd want to write into your raw files, I don't know if it'll write them into Phase raw formats, and again I don't know but maybe in PhaseOne's initial work on Expression Media they have made it open files into C1 without needing to write anything into the raw file. You may then question what role, if any, LR plays in the workflow.
Lastly, what role do the ratings play? Why not simply identify the items you want to process in C1, and then drag them from LR to C1's icon. There are also LR plug-ins (my OpenDirectly can open files directly in C1 and Syncomatic could copy metadata if that's the underlying issue).