I was told same thing - switch on ignition with key - don't have mine with me but I think it's all in the manual.
I had an extra problem last year - as well as the sleep mode situation I couldn't open the door with key either. I had had a replacement lock fitted (as window wasn't lowering that fraction when door opened) a few months earlier by local Porsche main dealer. They hadn't attached one of the mechanical linkages properly which had become disengaged from lock mechanism - though not known to me at the time. It may have ben like it for a while as I hadn't had a situation where I hadn't used the car for 5 days plus previously.
The car was stuck in gear, hand brake on and steering on full lock in my garage - none of which could I rectify. Main dealer (in Cardiff) said they couldn't come out to see it, I had to deliver it to them. AA said they couldn't do anything - ring Porsche. A further call to Porsche led to more disinterest. A local independent I rang told me how to pop the bonnet which I did - took me a while in limited space - and then at their advice disconnected and reconnected the battery. No luck. Same independent came out and with aid of jacks etc extricated car and recovered to their premises at my cost.
When problem diagnosed Porsche manin dealer agreed to resolve issue and collected vehicle from independent. Was offered a half price minor service in compensation - it wasn't worth all the hassle, time spent and loss of use. This was same place that charged me £700 for a MAF sensor replacement. Not been back since. Twice bitten ....
These were two of the very few sad tales I have had in 30 years of Porsche ownership.
