The First Amendment would be amended as follows:
“Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof, except that Islam is hereby deemed not to be a religion and is not afforded the protections of this Amendment or any other provision of law.”
How hard is that?
Good first step, now get 3/4 of Congress and states to ratify it. Oh, and what if they stop calling their religion Islam, and call themselves pastafarians.