If this tip has been posted please yank. Otherwise:
Create new Filled Region called "Clear". Set to transparent. Create new Model (not Drafting) Pattern of parallel lines that are spaced very far apart (100'). Associate new Model Pattern to Filled Region. Set the line weight to 1 and color to White.
Now you can create a filled region (using multiple boundary line types) that is effectively transparent.If you see one of the lines from the pattern just move it like you would any Model Pattern (that's why you don't want a Drafting Pattern - you can't move the pattern out of the way).
As it's a Filled Region - all the lines move together (nice) and you can have multiple lines define the boundary (nice).
In some cases this might be a lot easier than using the linework tool to selectively enhance the edges of a boundary (like in Interior Elevations).
Just an idea.
-Phil