Thanks for pointing me in that direction, but I'm not sure if that will work with what I am trying to do. The sharing tab isn't available under the bluetooth network properties.
I am connecting to a wifi router that is networked with certain devices. None of these devices need an internet connection, and they already have IP addresses assigned to them from the wireless router. And it seems like if I could enable ICS with the bluetooth connection, my laptop (the host) would want to assign other devices IP addresses on the wifi network.
On my laptop I am running software that observes and controls these devices through the wifi network. I want to be able to bluetooth tether to my iPhone so I can also access the internet from my laptop (and only my laptop) if I need to. I am not trying to share the internet with other devices.
I don't mind if ICS is the only way to enable this, as long as my computer isn't trying to assign IP addresses to other devices on the network. But it doesn't seem like it is an option for my blouetooth connection anyway.