I'm assuming you mean fit heated to a vehicle that didn't previously have heated.
Yes 'possible',
but in my mind very complicated, to do this to oem standards at least.
The simple way is to buy heater pads, off eBay perhaps. So pick up 12 volts from under the passenger seat perhaps, the battery is there as are spare fuse ways.
Mount eBay style switches somewhere,
strip the seats and instal the pads, not an easy task (I've stripped these seats).
I've no experience of the pads but I remember reading of a member who installed these to his rear seats (not Vi) and said they worked well.
For oem the switch pack at the front would need changing, although I know there is an easier way if the switch caps can be sourced.
Identify the supply point to the heaters, but you would need to run from the under bonnet fuse box to supply that. Then on to the seats.
It may be that the SAM would need coding by Star to make the facility available, I don't know for sure.
In short finding a Vi with heated seats is far easier.
These are rare in the Vito and much more common, but not regular, in the Viano.
As mine has the 2 heated front seats, and as is common the drivers seat is shot, I'm looking to instal ML164 seats up front.
It is an assumption that the heater will be directly compatable with mine.
I would need to run 12 volts from under the bonnet to the seats for the controllers.
As the movement controls and memory are integral to the seat there is no need to concern myself with door cards.
I did this upgrade to my earlier Vito but with ML163 seats. All movement and memory worked fine they are more comfortable, but the heaters aren't compatable w/o a voltage comparator.
I stripped the heaters out of my removed Vito seat and installed into the ML seat. It worked well enough but was a pain of a job.