If you've been doing H exclusively for a while (there is no bupe in your system), then taking bupe will DEFINITELY plunge you into pwd and it will be Hell and you will learn a lesson you will not soon forget.
The correct way to do it is wait until you are in AGONIZING withdrawal. Some people use hours. I don't. I say, wait until w/d begins, then wait, then wait more, then wait more, then when your legs have kicked enough to get a bike to travel a mile, then dose your sub.
There is another way. If you want a shortcut/not wait as long, you can chop your subutex REAL small, and take ~.25mg first. Wait an hour. That dose will partially knock off the H bound to your receptors. Do it again for good measure after that hour has passed (~0.25mg). An hour later, take 0.5mg. An hour after that, take 1mg. After 4 hours, if no pwd has presented, you can then take a large dose safely. The first infusion of small doses served to "gently" cleanse your receptors of the H.
The reason this is so is because bupe has a binding affiity to your receptors hundreds to thousands of times stronger than other opioids. That means that even if other opioids are locked in, intersynaptial bupe will outcompete them and knock them off, but often won't bind. This is what I imagine someone high on H being administered narcan feels like. The naloxone has nothing to do with it. It is inert and was placed in Suboxone formulations as a way to extend the patent and market the new product as being "unabusable", which it is not.