Most likely you are going to have to click the "request assistance" button in DTS, and note in the comment field what you want. Or, call SATO, but they'll probably just say "enter it in DTS first". Nothing good ever comes from DTS, ever. In a complicated routing like this, is it very possible SATO will find a more direct route, with the stopover, for less than DTS is quoting. THen again, adding a stopover may require point to point ticketing and SATO may be required to book SFO-FRA, FRA-BAH, which will likely be different cost than searching SFO-BAH. Good luck.