Such umbrella organizations exist -- they're called fiscal sponsors (http://en.wikipedia.org/wiki/Fiscal_sponsorship)

I worked at a non-profit fiscally sponsored by the Trust for Conservation Innovation (http://trustforconservationinnovation.org/), which is focused on environmental projects and takes 8% of project revenue.

I definitely recommend non-profit startups consider starting with a fiscal sponsor instead of trying to register as an independent 501(c)(3). You can always spin off later if necessary.