Normally you don't write in the rules what *is* allowed unless it's a specific exception. Generally, if something isn't in the rules, it's allowed. I could see in this case, though, that people might consider fake freeruns to fall under the definition of griefing. If that becomes a problem, it wouldn't be unwarranted to add a note in the Deathrun rules specifically that fake freeruns are not considered as such.
It's one of those things where I feel like it should be clear to people either way (like come on, *who* falls for fake freeruns and blames literally anyone other than themselves), but then again rules aren't written for people who can figure out every acceptable or unaccaptable behaviour just like that.