In this case I chose the second strain not to contrast so much as to complement: its musical material is different, but both have a "subdominant" emphasis at the beginning, the affect is quite similar, and so is the final cadence. The new strain is taken from the first of 2 German Dances, D. 769, and therefore contemporaneous with the numbers in D. 779. (The two pieces in D. 769, both 16-bar forms, are obviously meant to be a dance-trio pair.)
Note: The pairing of contrasting strains in these small waltzes is very probably the source of the paired 32-bar strains that had become the typical design by the generation of Johann Strauss, jr.