I have a leaf blower and that seems like the nuclear option for cleaning a PC.
As an aside, we have two dogs for the time being and they are very afraid of the leaf blower. All I have to do is point it at one without even turning it on and she scampers away. It’s almost as scary as the vacuum!
So in movies where someone has to crawl through an air shaft with fans, the hero usually plugs the fan with something like a crowbar. So I suggest ramming hairpins and chopsticks into your fans to immobilize them. I’m sure it will work!
Leaf blowered my case earlier today and it went really well. The liquid radiator was pretty much fully clogged and it’s now pristine. The only thing is the stuff that’s stuck to the acrylic itself wouldn’t come off no matter how hard I blew it. Wiping it by hand is the only thing that works. Same thing with the fan blades.