Eating wrapped up matzah

The din is that if you eat matzah wrapped in something ("karcho b'siv" - pesachim 115b) you are not yotzei the mitzvah of matzah. Rashi and Rashbam explain that the wrap does not work because "lo haya mamash b'piv", it is like the matzah was never in your mouth. The Mishne l'Melech in Hil Ma'achalos Asuros suggests that this may be true by issurim as well - i.e. if you wrap a davar issur in something and swallow it, you would not be chayav because that is not called derech achila.