Its true that even though guys claim to have installed cards which dont crossfire, you cant find a "how to do it" reference anywhere on the internet. One guy said he has done it several times but with no explanation.
Anyway...Here is the link to page 3 of the October 2012 article, where they used a CLUB HD 7850 royalQueen (Poker Series) GPU. They use it but don't get into any detail about the install.
I'm guessing this might be a GPU sold in the United Kingdom based on the name. I also see a 2GB version listed on the ever popular auction site right now and it out of the UK . I suppose if one 7850 works, others will too.
It's interesting that AMD is not getting the word out there so people know the 7850 will work with their A10 5800K. Maybe they will announce the compatibility when they release their newest GPU in June.
Here is where they do some tests, but it looks like they are not cross-firing it..yet I'm pretty new to this stuff, so you guys can figure it out based on what you see.
What initially drew my attention to this article, is that I have the same A10 5800K and motherboard that they used for the combination --- ASUS F2A85-V PRO
Then upon some further digging I found the approved list of graphics cards that will work (not in crossfire mode) with the A10 5800K and sure enough the HD 6950 2GB was on the list...so it can be done.