Blu tac works well for dry, solid stuff. Just don't be a brute.
Where Blu tac doesn't work so well IMO is to clean the mesh facing your ear. That one can get clogged up in skin oil / wax if your own ear anatomy means that it touches your skin and this will degrade the ANC and the SQ over time.
Apple's latest hardware revision has a recessed mesh in that place to mitigate that issue but I certainly hope this vent will be relocated or significantly redesigned in the APP2 to eliminate that problem entirely.