I can only assume there must be many aftermarket auto trim shops that can install heating elements in your Versa. I say this based upon the numerous times during new car shopping I'd turn to the sales rep and ask if heated seats are available knowing full well that in the case of the make/model I was looking at, it wasn't something the manufacturer offered.99.9 per cent of the time the rep would say 'yes' and when asked if this was from the manufacturer, they would admit that it wasn't but that it was something they have done 'locally.' Same thing for sunroofs if the model you are considering doesn't offer it.
I've never had heated seats installed by an aftermarket shop only because I fear they may not be able to duplicate the manufacturer's quality when it comes to re-installing the seat covers but that's probably an outdated concern. Like everything else, I'm sure it boils down to simply who you get working on your vehicle that specific day.
If your dearler can't suggest a source, I'm sure if you phone other dealers regardless of brand, they will be able to. Then I'd make sure the shop(s) you are considering actually show you one in process and of course the finished result.
It's unfortunate Nissan doesn't offer them from the factory, especially when you consider at that stage it probably doesn't add more than $10 to 20 to their cost and that both Korean marques offer them on even their cheapest models in this market.