Hi James, there is a new "RemoveAndFill" function in v5 that can be used for this case.

You can access it by selecting the face:



Then use Shift+Delete:



It's also possible to do an "untrim" to erase a trim boundary to uncover the underlying surface. That's done by separating out a surface so it's not joined and then select all edges of a boundary and use Delete.

Some info on untrim here, but Shift+Delete is more convenient:

http://moi3d.com/forum/index.php?webtag=MOI&msg=444.4
http://moi3d.com/forum/index.php?webtag=MOI&msg=9671.5

- Michael