First, the bypass of coolant to the ITB. The coolant circuit in the throttle body is to speed up the idle stabilization after a cold start. The coolant that runs through the throttle body warms up the quickest because it is recirculated (sorta like the heat riser system on carbed engines or like "carb heat" on airplane engines). Blocking the TB may only fool the ECU into thinking that the engine hasn't warmed up yet and it will continue to keep the idle high and continue to run a richer mixture. Obviously a richer mixture can cause some horsepower loss and even wreak havoc with your idle. If you bypass the coolant flow, the sensor inside does not see the temp of the coolant, and will cause the engine to run richer longer, and your engine will take longer to warm up and stabilize your idle. This is even more so when the weather is colder.

Also, this is like trying to use a spray bottle full of your own pee to put out a forest fire. The greatest amount of heating and heat transfer occurs in the intake manifold. This is where your intake charge heats up the most. The main reason being the heat via conduction from the head. The little piss stream that flows through the cooling jacket of the ITB has nowhere near the surface area or cooling capacity to even be effective in cooling down the intake charge. In other words, you can block it all you want, it's not going to do jack. It can, however, screw with your idle and your air/fuel mixture. Think about this from a thermal standpoint. Look at a front mount intercooler for a turbo, and all of the surface area it has with all the tiny foils, etc. That is the kind of surface area you need to cool the intake charge. Again, the ITB simply won't cut it.

The entire purpose of the ITB coolant jacket is to help in colder temperature, is to warm up the ITB just enough to it can get a stable idle after a cold start. After the engine is up to temp, it has no effect on the intake charge temp no matter what you do or don't run through it.