You could look at going with a small Linux computer, like a http://www.raspberrypi.org/ or a http://beagleboard.org/products/beaglebone%20black. It'd be more of a project to tie them into the ISY but should be doable with the right combination of software. The Pi is $35 and has 17 GPIO (General Purpose Input/Output) pins and the Beagle Bone Black runs $45 has can have up to 69 GPIO pins. In either case you'd connect in over the ethernet network and make network calls to the ISY to update variables.