Here is a quote for that fix:
The Witcher 2 only supports surround for NVIDIA - this fix enables surround support for AMD video cards. Attempting to use this fix on NVIDIA cards may result in flickering.
People may wish to use this to remove the black bars on NVIDIA, however without access to NVIDIA hardware it's difficult to test properly :)
If you experience issues with excessive blurring you may need to disable it.
So no eyefinity support, not even with a fix.
Yes, I understand that the game alone doesn't support AMD Eyefinity. However, with Flawless Widescreen or Widescreen Fixer that all changes. I'm wondering which version of the game (GOG or Steam or retail copy) should I buy so that the community based solutions will work.
Widescreen Fixer is touted to work with v3.2 of the game but I don't know which source that applies to and this post
(Witcher 2 Forum) is saying that it's not working for him at all.