I didn't actually try this, but it looks pretty easy.
In the file you mentioned I found this code:
Subject:
">
* <?=$errors?>
Wouldn't it just be a matter of changing this:
">
to this:
My first subject here
My second subject here
the value="" part is what will actually be used in the system as the subject, and the part between the > and is what the person would actually see in the drop-down box, they don't have to be the same. For example, you can do something like this if you want:
General Information
And in the system it will have "general" as the subject, but the person filling out the form would see "General Information" in the drop-down list.