I have been testing HA solutions at work for our SharePoint deployment and we are looking at using Microsoft's Network Load Balancer (NLB) technology that's built into Windows Server.  One of the options I saw when I clicked on a node I saw an option that said Drainstop and of course I found what I was looking for in TechNet:

When you use the stop command, either through Network Load Balancing Manager or the command prompt, any client connections already in progress are interrupted. To avoid interrupting active connections, consider using the drainstop cluster-control command, which allows the host to continue servicing active connections, but disables all new traffic to that host. For more information, see "Disable new traffic handling and stop Network Load Balancing" in Related Topics.

http://technet.microsoft.com/en-us/library/cc781186(WS.10).aspx

I looks like this is the idea way to stop the NLB cluster from routing information to a host that I will need to take offline for maintenance.