Those without the CO2 rig can just use a clean hand pump and a HEPA filter.
Honest to god though I don't see a compelling reason to worry about anythign in the air wrecking the beer.
This is a joke, right? A joke is fine but some less experienced readers might take it seriously.
For their benefit: The main reason for counterpressure filling of kegs or bottles is exclusion of air - in particular the oxygen in it. Having it displace CO2 in the target container and pushing it with CO2 not only insures that no oxygen can enter the beer but gives any in the beer an opportunity to escape.
If you are filling a growler to be consumed at a party you are going to that night you don't need to worry about air exposure but if any kind of shelf life is desired then oxygen is the main concern.
One of the main reasons for buying a CC fermentor is so that you can do CO2 CP transfer to keg (or bottle but usually by way of a keg) and have kegs that are good for 12 months or more.