I am asking on behalf of FluxBB, an open-source project I'm contributing to: We would love to offer "jobs" for this year's Google Summer of Code, but we completely lack the resources or the man-power to let somebody from our team be a mentor.
So my question is: are there any mentors who would take on mentoring for other projects or are completely free of any organization behind them that wants to benefit from the program itself?
Not a good idea:
Your best bet is instead to try to persuade your potential in-house mentors to reconsider, and go in under an umbrella php org. Aim for your in-house mentors to mentor one student collaboratively, with one mentor taking point position. People in the umbrella org will help a bit, mostly with admin, and reduce that part of the workload.