I just have an incredibly hard time imagining how I could nap on a yoga mat in my cubile without everyone else stopping to watch it like a circus, and my manger wanting to discuss why I am literally sleeping on the job.
There is a class of bosses who would accept that (obviously if you also stay twenty minutes longer & are salaried, they have nothing to lose). There is also a class of bosses who would not care how much sense it did or didn't make.
In an open office if it wasn't part of the company culture, few bosses will accept it. The political ramifications of having your employees sleeping when the VP walks by are too great (and, often, the manager won't even have the option to explain why it's good). I fully understand the benefits of napping, but I would demand employees to "get a room", for their sake and mine.
You can also sort of nap in a bathroom stall. It's difficult to fall asleep completely, but closing your eyes and resting your face in your hands, with you elbows resting on your legs, for about 5-10 minutes, can help you feel rested and refreshed. And nobody will ever know.
CAR:
I used to go to my car and take a nap. Kick the seat back, eye cover, maybe ear plugs and put the alarm on vibrate and in my shirt pocket.
Depending on someones situation and their proximity to their vehicle, if they drive.. It could be good.
YOGA MAT:
Everyone likes being hip and yogic. Buy a yoga mat. By tying yoga mats to napping it seems all so, much, more okay.
It's easy to lie on the floor, once you learn to nap on the floor you'll have the most refreshing naps ever.