BayAreaKiteboarding.com

Is there a kiteboarding location within a ~4 hour drive of San Francisco where it's possible to launch a kite from a house backyard & access the water from there?

Interesting question! I would say the following could be options...
Homes along the levy near Sherman Island (front yard access)
Homes with backyard access at Folsom Lake
Homes with backyard access at Lake Tahoe
Homes right next to Washoe Lake in Nevada?
There could be other homes on the Coast or within the Bay and Delta areas that have private yards that access the water, but probably too many to research.
For something out of the ordinary - Point Buckler
http://pointbucklerclub.com

Collinsville (its in the delta)
you could keep your kite pumped in the yard,
protected with kite cover of course

How sketchy of a launch can you tolerate? Plenty of places on the coast and inside the bay.

There used to be a VRBO rental right on Davenport Beach near Waddell, but I don't see it there anymore.
Santa Cruz has some on the beach, but usually the wind isn't adequate there.
Here's one on Bodega Bay: http://bodegabaybirdwatch.com/amenities/amenities.html
Stinson Beach has houses on the beach, but I've never kited there, so not sure.
Dillon Beach has places where you're on the bluff above the beach, so you could watch your gear while you take a break.
Cayucos and Cambria on the central coast are within 4 hrs. We stayed at a house on the beach in Cayucos a few years ago and launched on the beach 100 feet from the house.

stinson, i have done it from rental house

Lake Tahoe North Shore Kings Beach and Tahoe City but wind is not consistent at all up there. Maybe Halfmoon bay but season there is ending very soon.