It would be more convenient if the back translation was more integrated into the project plan, but the SIL Base plan has several tasks related to the Back translation. In what way do these not meet your needs? If I understood what you needed better, I could make other suggestions.
It is true that the person assigned to work on the back translation, must know the name of the back translation project and open it for themselves, but back translations can be in project plans. There is even an automated check that can be enabled to prompt the team that the vernacular project has changed and they should verify that the back translation is still correct.