You can use the Magnet system. Go to Library in LimeWire. Ctrl + click any file and select Advance > Copy Magnet-link.

The Magnet link might look like the one below. You can just enter the Magnet link as a regular link on your site. Please refer users too MagnetLink.org if they want to know what it is.

magnet:?xt=urn:sha1:7AU4CXDHJZRCYVSKYTNQJ4CVWCC6BK TQ&dn=ClamXav+1.0.1.dmg&xs=http://www.unmetered.org.uk/clamXav/ClamXav_1.0.1.dmg

In short:

xt = BitBrint or a individual identificator
dn = Download name
xs = primary source for file, here you can enter a web fallback adress. If LimeWire can't find the file it will use the weblink to download the file, but ONLY if it's the exact same file as you generated the xt with.

Alternativly you can use magnet:?kt=search+keywords