- Download Lion from the Mac App Store.
- Use Disk Utility to restore /Applications/Install Mac OS X Lion.app/Contents/SharedSupport to a USB flash drive.
- Download Lion Server from the Mac App Store.
- Grab the correct version of ServerEssentials.pkg by running curl “http://swscan.apple.com/content/catalogs/others/index-lion-snowleopard-leopard.merged-1.sucatalog” | grep ServerEssentials in a Terminal, searching for the line that corresponds to your version of Lion (it can be identified by looking at ./System/Library/CoreServices/SystemVersion.plist on the flash drive), and downloading the file from the link referenced by that line (it will look like http://swcdn.apple.com/content/downloads/21/09/11E53_ServerEssentials/yfLkxRYr8GczRPHKBSpStgMYT3kjRnKQRf/ServerEssentials.pkg).
- Drop the downloaded ServerEssentials.pkg into ./Packages on the flash drive.
- If after installing from the Flash drive, you are missing /Applications/Server.app, that can easily be extracted from the Lion Server Combo Updater (use the version that corresponds to your Lion version) using Pacifist.
More details here.