Exactly the same way Samsung, HTC are/were handling it.
Add to that, they need to sell Symbian for a few more years anyway.
Nokia essentially dropped Symbian two years ago.
Also, Samsung has gotten nowhere with their alternative OSes.
Funnily enough one of their alternative OSes that is getting them nowhere is Windows and they decided to focus on Android instead.
Nokia has become _the windows phone_.
I don't see how that is helping them. They had huge brand recognition. It used to be that 1 every 3 phones sold was made by them. Not saying that Elop was the source of all their misery, but the Windows Phone strategy doesn't seem to be helping them much.
As of now, Lumia accounts for 75% of windows phone sales.
The latter being around 3% of total smartphone sales, comparable to the marketshare of Bada OS two years ago.