Walk behind snowblower, won't start. Engine will run for a second or 2 if fuel or starter fluid is put directly into spark plug hole. Will not keep running. Fuel is clean.

It's your carb. Well, fuel delivery system.

Check your lines for obstructions, make sure nothing is blocked, apart from that it can really only be the carb.

Has the fuel been in it since last winter? If so, put in fresh petrol.

This. Even if you drained the old fuel and filled up with fresh stuff, the carb's bowl will be clogged with varnish and gunk...unless you did the good thing and ran it until it was out of fuel of course. That empties the carb of fuel, preventing it from gumming up.

You'll need to take the carb apart and clean the needle, jet, and all the little passages.

Also check for rotten seals in the fuel tap.

Can I just hook it up to an airhose and blow the gunk out? It seems like it would be a hellofalot easier.

you could try and just open the airbox, take out the air filter, hold the throttle open and use the air nozzle in there...but it probably wont do jack squat.

clean the carb.

You could run something like Seafoam through the carb. I've used it to clean small engine carbs quite a few times with good success.

Although its always worth learning how to rebuild the carb.

No, the gunk isn't just floating around in the carb - it's blocking the jets and valves inside, and it's stuck very firmly to the walls. Carb cleaner is the way to go.

Although its always worth learning how to rebuild the carb.
I know how to, I just don't want to have to. And I'm snowed in so I can't go to the store for carb cleaner. I have my doubts about the problem being junk in the carb. It ran fine a couple days ago.