You don’t have to lock yourself in a room etc. The vast majority of us, at least in that cesspit of “thinking” otherwise known as Silicon Valley, already spend 1–2 hours a day locked up — in a car. So all you have to do is turn your electronics off during your commute — no phone, no radio, no podcasts, no meetings, no music, no self-help nor how-to nor seven-steps audio books. You’ll have plenty of time to think, if you are not afraid of “unproductive time”.
How afraid are people of “thinking time”, at least until it becomes the latest HR approved Silicon Valley “productivity” fad and everybody claims to be doing it? You judge for yourself. When people in casual conversations ask you how you spend your time at work or “what you do”, tell them, like I used to, that you spend a third of your time twiddling your thumbs. Tell them you carry a notebook on hikes for jotting down an idea, tell them that you stop in the middle of a hike to spend time developing that idea. See how they react ;-) It all sounds a lot less full-of-it than locking yourself in a room for two hours on Thursday.
So I don’t actually think this will work — if you are mid-career, you are either a thinker already, or you are not. It is unlikely that you can train yourself to “think”. You only can think you can.