Well you would basically be creating a little still air tent. It could definitely work but it's not necessary. You can just turn off any fans or HVAC, wipe down the surfaces in your bathroom with bleach water or alcohol, and set a glovebox on the sink--if you have space on the counter top.
I usually take any towels, rugs, etc out, wipe down the bathroom, put everything I need for my project in, and then take a shower. Get out of the shower and towel down with a fresh clean towel, put the towel on the floor (makes for a comfy bath rug), and go to town. You can leave the bathroom door open while you run the shower so it doesn't get too stifling in there while you're working.
With this method I've been able to do agar work and spawn grains to sawdust without a flow hood. I don't get much contamination.
Granted, if you're just doing the basic PF tek you don't have to go to these lengths. You can do it in open air (you still want to turn off the fans and HVAC) and skip the shower.