back seat: Suppose that you're doing a regular mhd from YXU-YVR via MEX, the normal route would be YXU-YVR-LAX-MEX. However, if you look at UA YVR-MEX they allow for YVR-ORD-MEX. and if you look at ORD-MEX, then you can go via LAX. So, if the airlines allow you to do this, your mhd could be, for example, YXU-YOW-YVR-ORD-LAX-MEX and back. That one is just doable in a (long)day. In principle, you could just criss-cross the country for as long as you have time. I'm going to check with my travel agent to see if this is permitted and I'll post the answer.