do you have sketchup pro? if so, you could try using .3ds exports from rhino then import that into sketchup… .3ds has a few limitations (such as polycount per group is ~65k) but it’s the fastest format for getting things into sketchup from rhino.
if you don’t have sketchup pro, you can try one of the OBJ importer plugins for sketchup like this one:
the problem with that one is that it’s painfully slow (as in, a few hours to bring in a decent sized model from rhino)
here’s a newer one which i haven’t tried but read the comments in the link to get an idea of how sketchupFree users feel about the $100 price tag.
it’s possible we’ll see a Collada exporter (.dae) in mac rhino soon in which case, that will probably be the best way to go between rhino and the free (and pro) version of sketchup