To do this, you need:
-A simple cage suet feeder. They sell them at WalMart for around $2. I got mine from Home Depot for 3.
-A thin-ish sheet of plastic. Not so thin that cut edges will be very sharp, but thin enough to cut. I used a cutting mat for food. You can purchase a 3-pack at WalMart for about $3.
-Carpentry (or Utility) scissors
How you do it:
---Update (05May2009): Instead of going through all the trouble to create the plastic guard, just using the plastic that the suet comes in might work just as well. Haven't tried it yet myself, but if you'd like to be a ginea pig, go right ahead, and make sure you send me a note telling me how it works for you! =) If you do decide to do that, you can skip this first part and skip ahead to the large purple asterisk (*) farther down.---
First, you want to measure the dimentions of your suet cage. I assume this is pretty universal, and here are my measurements below. (in inches) I didn't take pictures as I went along, so I hope you won't mind my crude illustrations.
Then, you need to cut out a peice of plastic using the layout below. (tweaked with your measurements if need be) If anything, go a little small because this is going to fit inside your cage to block all side except what will become the bottom. I would recomend drawing all the black lines, not just the outer ones, so you have a guide to follow in your next step.
You're now going to score the lines of the inner 4 3/4 x 4 1/4 rectangle so that ths side flaps can be folded. (I used a utility knife for this.)*
Now we need to hang it so that the accesible face is the bottom, not a side. If your suet feeder is like mine, then it hangs from a chain attatched on what we want to be the side. (Seen from what is supposed to be the top in the picture below.) It's a rather long chain that ends in an "S" hook.
We need to detach this "S" hook. You can detatch it by opening either the hook here:
You are now going to attach your "S" hook to the center of your chain.
Last, but certainly not least, put in your plastic guard and suet block. I turned it around since taking these picture, so that it opens at the bottom, for easy filling, and that's worked well so far.
It's not as pretty as the one up in that link at the top, but hopefully it'll still work. :)