I don't really think there's any way to not startle/disturb a snake when waking them from a nap..... that being said, whenever I approach any snake (slumbering or not) I give them a light stroke down their back, usually starting at the halfway point of the spine, to let them know that I'm there and I'm not a threat or food. Some get startled if they're not expecting it (or asleep) but I've so far never been bitten that way.