Hi NightCabbage, that is actually something I've been thinking about recently and I have some ideas on how to add that in the future.

In the meantime though you need to use a combination of tools (like Offset, Extrude, and Booleans) to create that kind of stuff. See here for some examples:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2088.5

- Michael