No, you cannot exclude based on the generation like that. You would have to exclude based on some other criteria, such as telephony (this would exclude iPod touches and iPads), or gps (this would exclude iPod touches and non-cellular iPads). There are other things as well that would give you different subsets of devices that you want as well. But there is nothing that you could do that would specifically eliminate only the 4th gen iPod touch.
You could always require at least iOS 7, which of course would exclude some users of newer devices who haven't upgraded, but it would make the minimum iPhone supported be the iPhone 4, the minimum iPad supported be the iPad 2, and the minimum iPod touch supported be the 5th gen iPod touch. This is the only thing I can see actually working to accomplish what you want here.