ISBoxer.com

The official download links for LOTRO recently changed so that all of them download the Happy Cloud installer. The installer now gives you the options for selecting between Low or High Resolution, as well as Progressive or Full Download. For ISBoxer to work, you must install using the Full Download option. Low/High Resolution is up to you, but for best performance while multiboxing we do recommend Low.

Luckily the Steam client seems to download almost everything except for the last few megabytes of updates that the launcher uploads. After you've downloaded the game you can turn of Steam if for some reason someone doesn't like Steam or something.