You can do this without SDK source changes.
Upgrade an installation of SDK to use SDK release 21 release candidate 4, using the new slick way to install previews/release candidates:
http://tools.android.com/download/adt-21-previewhttp://tools.android.com/preview-channelCreate a sys-img.xml file via manually editing an existing example. Have it point (via URLs) to the system image zips that you want to use.
You can find an example xml file at
http://www.mips.com/global/sdk-sys-img.xmlThe zipped file needs to have a certain structure of folders and files. Follow the example of
http://download-software.intel.com/sites/landingpage/android/sysimg_x86-16_r01.zipThis will involve manually gathering files built from both standard android makes and makes of sdk. (For both, you'll need a full Android src repo)
To get the sys-img.xml file used by SDK, go to SDK Manager, Tools, Manage Add-on Sites, User-Defined Sites, New. Ignore the warning about system images. Name the xml as either a http-hosted file on your intranet, or as a local file. The spelling of the last part of the name is important; it must end with 'sys-img.xml'. Hit Close. On SDK Manager's main panel, lower right corner, is an icon for seeing SDK Manager's log window. Click on it. You'll see that SDK Manager attempted to open and scan your new xml file, and found it, but didn't get anything useful from it in its first attempt. That's a bug in the release candidate. Exit SDK Manager (and Eclipse, if you are using it). Re-enter SDK Manager, and you'll see in the log window that it is now parsing the xml file and noting the name of your system image zip file. If it liked it, the system image should now be showing on SDK Manager's main panel as an available (but not yet installed) system image, for whatever Android ABI level you claimed. You can then install it.
This will only work for cpu types and library abi conventions that SDK is already expecting, ie one of arm, armv7, x86 atom, or mips.
There is an older way to access system image files, that works with older releases of SDK also. This was and is still being used for Intel's first system image for API 10, Follow the example at
http://software.intel.com/sites/landingpage/android/addon.xmlThis involves a larger zipped folder structure than is used with sys-img.xml links.