I haven't seen the portable version listed on the LW site for ages. But I did find this link:
LimeWire Portable | Download LimeWire Portable software for free at SourceForge.net
Bear in mind it's a Beta version, so might have some bugs.
And here's a link to the LW wiki with info about using a portable version:
LimeWire Portable - LimeWire
See whether that helps