Yeah i wonder the same.
I have been looking for a way to do it by hand but faild so far.
And i dont see an option to import saves via GOG galaxy....
Any help will be more then welcome
EDIT.
This may help
All you need to do is place your Witcher 2: Assassins of Kings save files in the following folder:
C:\Users\YourUserName\My Documents\Witcher 2\gamesaves
If you happened to play the Steam version and you do not have these folders at the above address, simply create them yourself and then just copy/paste all of your favourite save files in it!
Thanks go to Engagerade for this information!