In California having your keys in the ignition, with the engine off is enough to convict you of DUI in this scenario.
Regards
If I'm not mistaken, just having the keys in your possession or having access to them is sufficient here in California.
When I needed to 'sleep it off' on a few occasions in Felton, I'd park in the bowling alley lot and flip my ignition key through the slot between the bowling alley's front doors. Since I had no access to the keys until the restaurant opened the next morning, I knew that I couldn't be charged with DUI. (Of course, if the sheriff on duty was in a pi$$y mood, he could always write me up on a drunk in public charge.)