There are a few commands that don't have buttons but that you can set up on a keyboard shortcut, they are listed in the command reference section of the help file here:
http://moi3d.com/2.0/docs/moi_command_reference10.htm#Additional%20commands

I think you want the Rebuild command:
http://moi3d.com/2.0/docs/moi_command_reference10.htm#rebuild

Join your 2 curves together and then you can run Rebuild on it to construct a simplified single segment curve out of it.

- Michael