How do I change folder icon for custom folders?

Here's my dilemma: In Mac OS X 10.5 I want to change the icon of select folders or extra folders but not by pasting an icon via the get info window. I have been able to replace the standard icons of folders that are already present, such as the "Applications" folder, the "Users" folder, the "Library" folder, etc. What I'm looking at doing is attempting to continue this replacement with other folders, such as "Application Support", "Caches", "Preferences", etc. There are no folder icons for these so they just get the generic folder icon. I have tried putting in an extra array in the /System/Library/CoreServices/CoreTypes.bundle/Contents/Info.plist file under the section "CFBundleDocumentTypes" and added the extra icon into the Resources directory for CoreTypes.bundle, but that doesn't seem to work. Does anyone else know of a way to do what I'm looking for?