Lol! Ok, your not 'getting it'. let me try again. Your gauge measures the air/fuel ratio, it does not control it. Your air/fuel ratio is controlled by the sensor in (refer to your pic please) the number 1 bung hole. IF you remove that sensor, then your ECU (which controls your fuel injectors via input from the sensor in #1 hole) would have no reference to know how much fuel to add or subtract. I suspect that with no input, it would just keep adding fuel in an attempt to get some kind of reading (would it simply assume no fuel? That is what I am unsure about). Regardless, you car won't be able to run without sensor #1. Sensors #2,3 are for measuring the health of your catalytic converter. Note that sensor #2 resides right in the middle of it in the 'canister' portion (well, actually, that is an assumption as noone has ever taken one apart to know if it is in the cat or right before it. but based on it's location and the size of the canister make up your own mind). Regardless, it is a very poor location for a wideband as you want the exhaust gases flowing in close proxity to the wideband sensor. the canister is to big thus 'diluting' the mix. Hence, your only location left would be after the cat near #3. But as you already have a sensor stuck in the pipe at that location (assuming you keep it thus avoiding having to rig up a cheater), that leaves you with only the flex pipe or somewhere more 'downstream'. Typically, you would locate a wideband sensor in the collector of the manifold anyway (where the gases come together from the exhaust ports). So that is really your only option as regards the stock mani-cat.
Better? [cheers]
add > I read what your wrote about heatsinking the wideband. Discounting that you cannot drill and tap a bung into the cast material, I think there wrong. See, aftermarket headers are made from tubular steel. Hence, they dissipate heat much faster than a cast unit. That being known, If you were to add a heatsink (such as a piece of copper on the wideband sensor), it would heatsink the entire cast portion of the upper manifold (as it is coolest, heat would flow to it). Tween you and me, that's a lot of heat. And if your sitting at a stop light, you don't even get the advantage of airflow. So without that, the wideband is going to cook.