I guess I'll just need to get my students used to the idea that exam scores will not show up with their quiz scores.
The 'Outside Events' resource sounds like the external graded item you are planning. If it would sort students alphabetically, then I've have a reasonable way to enter grades right now.
Then again, some of the default sorting in moodle makes little sense. One example is when you list users. The default is by first name. I don't see the logic in that.