There are sights that are designed to be used with both eyes open at the same time. It works kind of like an iorn sight system on a gun where there are two items. First is a whole about 1-1.5 inches in diameter and you line this up withyour existingsighting system somehow...
Something like this....
http://www.cabelas.com/prod-1/0014655416001a.shtml
Where both eyes are opened b/c the new item has a very large diameter in comparison to a peep sight.