RTF carriage returns?

I now understand that spaces are necessary for MMD->HTML returns, as in :

Spring 2012: Tu, Th 12:00–1:50pm, ABAH 245~~
Instructor: Me

Where the ~~ is two spaces, and then I pressed the return key. But this doesn’t work on MMD–>RTF. How can we accomplish the same thing in MMD for processing straight to RTF?