I assume you mean the facebook widget? sorry, no idea about that, though I assume that the widget spawns a separate process periodically to do an https session to the facebook server to fetch any updates, so if you can track down the call and it's possible to hack it to use tsocks then you are in luck?

Probably best to wait for someone who knows about how/where widget-created processes get launched on n900 to let you try to proxify it properly though :-)