Yeah splicing the temp gauge into either wire of the 2 wire sensor up front would throw off both the ecu and your temp gauge reading. Very possible you would even burn up the ecu. The suggestion to tap a hole in the stat housing is the way I would go. The only issue there is I think it's a pipe thread for those sensors, slightly tapered, not sure what size, or if it would leak if you used a standard tap. I would try it with some thread sealer, worst case scenario if you screw up, that housing is pretty cheap.