LAX-SFO-EWR-IAD-ATL-IAD-ORD-SFO-LAX, for instance, would generate circa 22.5K milesfor about the same price, and on UA metal rather than US. The EWR-IAD segment would be Y. It would take a whole day of flying each way, however (leaving at 6 and arriving near midnight for SFO-ATL and leaving around 9.00 to arrive at midnight in the other direction).

The SFO-MCO can also be maximised by routing via PHL rather than CLT and connecting at both PHX and LAS, generating roughly 25K miles.
For these kind of itineraries, you might be better off booking on Orbitz rather than the airline's own site. Most definitely so for US itineraries, as the booking engine for multi-city itinerary is crap at pricing correctly.

It makes sense to play around with ITA when searching YUP fares or similar, leaving the check availability box unchecked to research theoretical itineraries. Once you have found it, you can then start searching dates by re-checking the availability box.