You can build a stopover in DTS (and without calling SATO) simply by booking your flights as SFO-FRA on the appropriate date, and then booking FRA-BAH on the appropriate date with the desired delay at FRA. However, as noted above, you need to ensure that the stopover will be allowed/approved under the JTR policy.

It's likely this will result in separate ticketing for the FRA-BAH flight(s), and it may be at significantly higher cost compared to booking using the SFO-DEN and DEN-BAH contract fare prices. Additionally, the separate FRA-BAH ticket might not be on a Star Alliance carrier depending on what flights DTS finds for that routing.

Your best bet is to call SATO and have them check to see if a stopover is allowed at FRA under the fare rules for the DEN-BAH contract flights. If it is they should be able to reserve it for you immediately.