Zax sums it up pretty well. There is no off switch or function. You could pull a fuse but there is no dedicated fuse so you'd be shutting other functions off as well. You could also disconnect connectors somewhere if you could find them but I suspect the same 'no dedicated connector' notion would apply.
That's the catch. You either shell out the money for the TPMS on new wheels or you learn to live with the light. I run my summer tire set up with no TPMS and my winter set with the stock tires with TPMS. It bothered me for maybe acouple hours then I don't even notice it.
The Ateq Quickset tool was the best $130 spent for having properly functioning TPMS in both my summer and winter wheelsets. Pays for itself if your local shop charges for a sensor reprogram and you can store multiple vehicles on it. I figure my tires are the only part of the car that touches the ground so I invest in good rubber and like to have fully functional pressure sensor system.