Rcord with it on and playback with it on. It should be ok.
But a better way for making tape dubs of a clean original (CD, good LP etc) is to get a great quality chrome tape like TDK-SA. (71 db S/N ratio) and record as hot as you can. Very frequent peaks at +3db. Because the signal is so hot, the playback volume can be very low. If it is 71 db or less you won't hear the tape hiss on a good tape.
Test. Put the blank tape in and listen with headphones. Crank the volume to hear loud tape hiss. Lower the volume so that you don't hear any tape hiss. Raise the volume to the point where having the dolby on or off makes no difference. Record as hot as you can and playback at that (low) volume.
No tape hiss, no muffled NR.
Works best with night time headphone listening.