You'll probably be ok putting the fermenter in a rubbermaid bin filled with water to a little less than the level of the beer. That could be 10 more gallons of water + 5 gallons of beer so it's going to significantly slow down temperature changes. The stick-on thermometers are pretty accurate if don't get wet and could be a good indicator if an ice-pack should be put into the water. That thermometer would need to be on the fermenter below the level of the beer. You could also add a little bleach to the water if it's going to sit for weeks.
Really get the temperature of the wort down below 64F (mid 50's would be more ideal), match the water temperature to that, and pitch the yeast cold. It probably won't be too hard to maintain your fermentation temperature for 3 days and leave it after that to the basement temperature or possibly take it upstairs (68F-72F) to ensure attenuation.
I've read some people use a towel draped over the fermemter with the system described above. It could help but isn't going to work without a bin full of water to keep it wet and reduce temperature swings by having a larger volume of water.
