I don't mean to bump an old thread, but it looks like there hasn't been any progress on a fix for this from Hi Rez. I have started a thread on their forum about it and if we can get some traffic to it they might listen. Here's the link.
http://www.ascendforums.com/topic/114-unplayable-for-eyefinity-owners/
Uhm, I don't mean to burst your bubble, but those are fan made forums. Here's the real forums.
http://forum.hirezstudios.com/phpbb/viewforum.php?f=250
And yes, it would be nice to play this game in glorious surround! There have been, however, threads on it before. Hi-Rez said we can work on a fix if we share the code to said fix to them. (They want to "approve it.")
Everyone's probably busy, so we are probably going to have to wait for dopefish to work on it.