In the FFS DLC do you have access to the Claptrap Store or the Safe? Or once in the DLC do you find a Fast Travel Station and go to an earlier BL2 level so you can have access to previously saved weapons?
You can always travel to Sanctuary from any FT location in the DLC at any time. Bit of a plot loop-hole, but what’s a little bit of time-travel on top of instantaneous digistruct travel?
Once you secure the back burner you’ll be able to use the fast travel station there to travel out of the area.