I just use an old A4 envelope folded in half. Works a treat. I found that plain A4 paper wouldn't be picked up by my optical mouse that well and it would jerk around a bit.
In the past I've bodged a resistor onto a fan cable then used a wrapper from a pack of fruit pastilles to cover it up by taping it around it at both ends. Worked good for months until I redid my cabling and got so fed up with the whiny little fan (reason i resistored it in the first place) that I tored the cables out of it.
Going to make my own fan hole in the side of my Antec Titan case door when the 92mm fan arrives. Not sure whether it should be an inny or an outty though. I'm thinking inny as there's only 2x80mm fans at the front blowing air in while I have a 120mm exhaust, the psu and the 2900XT blowing air out. The fan cover will be from the internal fan cover from the psu that I had to take off to get that needed 2mm of room for my Noctua CPU cooler.
Right now in my case though the biggest botch job is the 80mm AC-7 fan stuck to the back of my 2900XTs RAM heatsink plate by double sided sticky pads to blow over the noctua NB cooler as the P5N is a hot mother..
