This can absolutely be done. The first question is whether you want to disable the node as a global object or within the context of a specific pool (ie. a pool member). I've got some samples in the iControl CodeShare that deal with the later. It shouldn't be difficult to convert that script to use the LocalLB.NodeAddress interface instead of the LocalLB.PoolMember interface.
Check out the PowerShell topic in the iControl wiki and search for PsPoolMemberControl for some ideas.
http://devcentral.f5.com/wiki/default.aspx/iControl/PowerShell.html
There are also a bunch of articles in there on tutorials on getting started with PowerShell and iControl as well as how to use various interfaces.
Let me know if you get stuck...
-Joe
Nimbostratus