Can someone help me remember how to use advanced routing codes in Hipmunk to force a layover somewhere?

More specifically, I'm looking to do an open jaw trip from LAX, SFO to HAN and then return NRT, HND to LAX, SFO via GUM.

I thought I just had to do TYO::GUM in the from field, but that doesn't work. I used Hipmunk last year when I went to NRT to force a layover in HNL and then used same day changes to stay in Hawaii for a bit. I'm hoping to spend a day in Guam with the same technique this time.