If you insist on not rigging a cheap quar setup you could use a margarine tub clipped to the inside of the tank. Dump the contents of the bag into the tub, clip the tub in the tank, and pour a little tank water in every so often. After at least doubling the quantity of water pour the contents of the tub into the net, then add the unquared fish into your tank of healthy fish.
If you aren't going to quar you may as well add the bag water to the tank, and learn early on why you should have a quar setup.