I was having the same problem equipping dual Colossal Skull-Clad Cleavers for my fury warrior, but I found a solution.
Initially I had +85 attack power on both but I had my guildmate change one of them to +50 attack power so that the following solution will work.
If they're enchanted differently, find out what their exact item id's are. Equip both and run this once:copy and paste the following line into your chat box in-game.
/run local function id(s) return string.match(GetInventoryItemLink("player",s) or "","(item:.+:%d+)") end ChatFrame1:AddMessage("MH:"..id(16).."\nOH:"..id(1 7))
It will display something like this :for duel wielding colossal skull-clad cleavers one with +85 attack power and the other with +50 attack power gave the following results. If you use identical enchants you will have the same problem as before.
MH=item:37852:3828:0:0:0:0:0:0
OH=item:37852:1606:0:0:0:0:0:0
Using those exact item id's you can tweak this macro to toggle 2h and the two same-named weapons:
/equipslot 16 item:37852:3828:0:0:0:0:0:0
/equipslot 17 item:37852:1606:0:0:0:0:0:0