R' Daniel Eidensohn asked: <Does the mitzva of hearing shofar require guf naki? The Biur Halacha in Siman 588 (Shama tes tekios) discusses this issue, he is mistapek and then he quotes a Mateh Efraim that b'dieved you are yotze. RSZA in Halichos Shlomo (perek 2 sif 17) is matir if you have no alternative.