You're overthinking this thing. You will NEVER get a STAR in a C172, especially to a class C airport like OAK. You can probably get any practice approach into 27R. 29 would be iffy since it's the part 121 airline runway, but during off peak hours (especially the middle of the night) you can get approaches into most big airports, even the biggest class Bs. The one thing to watch out for is that the final approach segments between 29 and 27R get close to converging, so that may be a factor in their limiting the availability of a 27R approach. I'd highly doubt it though, Norcal Approach is usually top notch and professional.
I've never shot any of the approaches to 27R, but I have done closed traffic on the north field a few times, and they bring you in over lake Chabot from the SE to keep you well clear of the 29 arrivals and HWD. From the NE, the VFR entry would be via the Mormon Temple in the Oakland Hills, but IFR would be radar vectors (possibly as far south as SUNOL). Go up and ask Norcal approach sometime. The worst they can say is "no."
(And if you want to avoid rejection, I'd suggest calling Norcal approach and asking what the best time would be for them if they could accommodate that.)