@
Breaking Dawn it might be a bit difficult since it would kinda be impossible for the high ranks to not know since... he would be right there.
how i sort of was able to pull it off when i had dusk sneak into a past gathering was by utilizing shadow fiend combined with her masking her scent and hiding behind some of the seastone rocks on riverclan's side of the territory! even then she still ran the risk of someone leaving the gathering early and spotting her, but afaik that didn't happen