If you have any trips coming up between now and then you could pad your segments to get extra flight credits. They're offering double credits to/from MDW or BWI right now. Also, several west coast to MDW flights are $79 OW+ and several midwest to MDW flights are $39 OW+, so SAN-MDW + MDW-XXX would earn you 8 RR credits roundtrip (vs. 3 RR credits for traveling SAN-XXX roundtrip).

I assume from your name that you are flying out of SAN, so it wouldn't make sense for you to fly to MDW or BWI just for the segments, but if you were already planning a trip to the Midwest or East Coast anyway, you could certainly add an extra 5 credits as described above (or even more if you wanted to do something like SAN-MDW-CLE/CMH-BWI-XXX).