I think the way a lot of other people would do this is by making it a hosted re-brandable application with a subscription fee. JotSpot is a good example.

This removes some of the biggest obstacles to adoption because the customer doesn't have to worry about installing, upgrading, security, maintenance, etc.

For the larger customers who must have the machine inside their firewall you can alway role out an "Appliance" version something like the Google Search Appliance.