I'd say bite the bullet and set up a qt. Just go to Petsmart and buy a crappy 10 gallon glass aquarium with a simple heater, filter, and light. I'd also suggest an air bubbler or small powerhead for circulation My guess is you can get all that for about $50 if you buy one of those little 'starter kits.'
Put something in there for the fish to hide in, like a piece of PVC pipe or the like. No sand. No live rock. Then fill the aquarium with water from your own tank (like you're doing a water change). Give it a day or so with the filters and heaters running and you should be good to go.
The thing is, if you're pulling out your live rock and inverts and putting them into a rubbermaid, that's a lot of trouble (remember, you have to keep the water warm and circulated) and really only gives you the hyposalinity as an option. If you set up a qt tank, you can do hyposalinity, but you can also do other treatments if that's not working that would certainly harm your inverts. You can't do those treatments in the tank, because the chemicals will get into your sand and rock and your inverts won't survive when put back into the tank.
Get a QT!