How do you exclude spec files from a diagram?

I was trying to use the diagram tool for my project but when I run it it includes all the spec files making the diagram useless, I really don't care about specs for this particular diagram. The documentation seems to suggest that I should be able to use a custom scope to control the diagram tool's scope however after creating a custom scope that excludes specs there is no place to apply it to my diagram. If I go into preferences and try to set the scope there my custom scope is not visible. There has to be some way to filter files you don't want no? Without that ability diagrams are terrible.