I found you can create the phone contact with ringtone, link to the google contact, and then unlink the two and remove the phone contact. Seems to also work for those that don't want that extra linked contact. And to make this weirder, I've found that assigning ringtones to contacts (either via Ringdroid, or linking, etc) didn't seem to work for me until after the phone was restarted.
Did I miss reading how you can get all your google-based contacts set to phone contacts? Personally I only want custom rings for a few folks so the above method I've done works good enough for me (and creating short ringtones from .mp3 files via ringdroid is PERFECT IMO).