I get so stuck on M's as well, especially in very pressuring social situations! One technique my speech therapist suggested is using the slide technique so you basically would prolong the 'm' on purpose by saying it as *Mmmm*onday for a few seconds that apparently listeners won't really care to nitpick on that. It depends on how you feel if you'd say it as M-m-m-monday like myself, or if you'd prefer a smoother transition into it. Second could be that you can pretend you're about to sing out the word that there's a lot of evidence of stuttering reducing a significant amount when singing over some words that you follow a rhythm and it puts you at ease, requiring a lot of air from the lungs.