Get some garden wire from Screwfix, £4 for 15m of the stuff. You will not be able to make it spring or anything, but it is stiff small gauge wire that you can make a loop through the fan holes and around a heatpipe in the cooler, then twist the free ends of the wire to complete the loop and make it tighten up. Then snip off the excess. Similar idea to Pastymuncher's twin and earth solution, but likely will be smaller gauge and thus easier to manipulate. Either that or some thin elastic bungee cord from an Haberdashery shop to do the same thing.