You would be better off to ask on the BA forum about the intricacies of BA award rules. Backtracking means a change in the direction of motion (from east to west, for example). BA imposes these rules to prevent having too many stopovers on a ticket, and some routings are impossible. Your options are to redeem a Oneworld award on BA (different rules), or to redeem on a different FF plan (not BAEC). You'd have to meet the rule requirements. I suspect there is no way to fit in the DCA stopover within the BA rules for the award that you are using.