What you will want to do is to take the time to block out small sections and apply the numbing cream to just the small area and cover it with plastic prior to your appointment beginning. This will allow you to be ready for work when you get there. Once you start work, you uncover the prepped area, and apply cream to the next area and cover with plastic, and let that numb up while the work is being done in the area prepped for starters.
You may want to make a grid that has blocks about the size of your hand, or half that depending on how much space your practitioner can clear in an hour.
The problem people have is putting too much over too large an area at any given time, and letting it sit for too long.
The deaths involved with using these numbing creams occurred due the persons covering half their body, and/or including mucus membrane tissue in the occlusion and letting it marinate for 2 hours or more. This can be easily avoided.