09-05-2011, 03:59 AM
You just need to have your keyboard/mouse/power plugged into the MBA and it will not go to sleep when you close the lid. The Apple Store employee must have missed this (how many years now?) feature:
Requirements for closed display mode:
http://support.apple.com/kb/ht3131
Requirements for closed display mode:
- Power adapter
- External keyboard, mouse, or trackpad
- External display
http://support.apple.com/kb/ht3131