I would hesitate to use a fruit puree because of the fluidity of the puree (like strawberry or raspberry) - it will make the batter runnier and I'm not sure the flavor would be sufficient; if you do not have extract or oil in the flavor you want (much more flavor and very little change if any to the batter consistency), you could also use fruit powder in the batter (mix it with the TPT) or put the fruit flavor in the filling and leave the shell as is but with a bit of color from food coloring.