It is recommended if your iMac is under warranty that you contact Apple care and have them resolve this issue. If your computer is not under warranty proceed with reasonable care. While the ifixit team would like to accommodate you and provide a guide with pictures of this procedure for your specific model there are none at the moment. Your best known method to solve your problem is to loosely follow the procedure, for the 27", in the link you provided. In following that thread several people have successfully done this repair on their 24" and have stated that the repair is easier on their model. Hopefully you will find the same to be true. Credit for this procedure goes to Oggy & lefterisgr of the MacRumors Forums. This repair is not for the faint of heart, but not extremely difficult either.
1. Remove the glass, unscrew the 10 torx screws, disconnect the 4 cables that attach the LCD panel to the boards. Remove them, but be very careful, especially with the wide flat cable that's close to the middle of the screen - it's very easy to damage that connector if you're not careful, and put the panel on a soft, clean flat surface facing down. Follow this guide.
2. Unscrew 8 screws holding the frame to the panel. Some of them are beneath the cushions. They are different sizes, 2 of them are shorter, so keep track of that. This guy came to this part http://www.youtube.com/watch?v=BNWASktH7.... Watch the video!
3. Remove the black plastic tape from the bottom. Remove the metal tape from the corners. You will see the 3 places for "pry opening" the frame. There are two more that you don't see on the top side. They are beneath the frame on the sides. You have to remove the metal tape in the corners in order to see those places. Look closely from the side. They look like small dents in which you put a flat head screwdriver. Don't pry it yet. Using a razor slice the tape right next to the metal frame - between the black plastic and the external metal frame. It's easier than it sounds.
4. When you're done with that you will see some more prying places for releasing the frame. 5 on each side.The display must be vertical for this part of the job and it helps if you have a second person holding it. Using a small flat head screwdriver pry one point at a time.You want to pry between the metal frame and the black plastic, don't pry under plastic. Try to find the prying dents it will be easier to release the frame. Rotate the entire assembly as needed. There is no reason to open the tin plate that covers the board. You do need to unscrew the 2 top screws so this plate so that it releases from the frame.
5. Once it's loose, put it back face down and tilted it from the bottom. Just crack it open. The top side is connected to the logic board. Be gentle. Don't remove it all the way. The LCD's glass stayed on the bottom and you can squeeze a hand in to clean (using a DRY Apple's cloth). There will be dust on the backlight, the LCD's glass and the panel.
6. Close it and put the frame back. It snaps back easily just be careful with the top where the connections are.
It may be easier to snap back the LCD to the frame while vertical.
7. Put the screws back on the frame, place the frame onto the iMac and carefully re-attach the cables. screw the frame back, clean your fingerprints off and snap the glass back on.
Picture by lefterisgr MacRumors Forums