are they uploading it to their site on their own? With their own hosting and player? Or are they using VIMEO or YOUTUBE or something similar? Also is the footage HD?
If YOUTUBE or VIMEO, I’d just use the preset in compressor/quicktime. If it’s their own hosting, an H.264 compressed down to 1280×720 with a bit rate of around 10,000kbs (lower is probably best) should be fine.
From Final Cut Export a full res movie
File>Export>QuicktimeMovie…
Then drag that Quicktime into Compressor and drop on the settings.