No, not with one unit since the 7xx boxes will not record and play back at the same time. I have "overdubbed" using two 7xx boxes; one for recording and the other for playback. After tracking I had to sync the tracks in a DAW but that is no big deal. Of course I did not have to use another 7xx for playback; I could have played back the WAV file on a computer and that would have been good enough I suppose.
Over on the SD forum people have been requesting overdubbing capability, (on the 788T in particular) but the hardware will not support it.