You can also try just randomly searching your city pairs with a Saturday - Monday or Tuesday trip. I found out about these fare sales by random chance flying my sister in to DCA from CVG one weekend a few years ago.

I was prepared to pay a pretty penny for a last minute CVG-DCA-CVG trip, Saturday - Monday, and when the fare showed as only $166 all-in I thought I hit the jackpot. I say this because I did not use any particular fare sale link on (the old) delta.com, just found the sale by random chance in the standard Delta booking engine.

Good luck.