Unfortunately, not everybody can realize this. Most people are so connected to their physical environment in their conscious state that they just can't let go of their conscious connections. I guess all of us are caught up some way or the other.
There are many ways to train and access the subconscious. Musical performance training is one example. I have used alchohol to get some creative brainstorming done. Yoga and Bhuddism have centuries of tradition centered around exploring the subconscious.
People can learn to meditate. Brain scans of people who just learned "fixed point meditation" (where you stare at a dot and tune out your environment) showed up nearly identical to experienced practitioners. The only difference was that the inexperienced people couldn't hold the meditation for very long. But they appeared to be doing it right. [1]
I've never tried meditation, but I do notice myself sometimes just staring out the window for a few minutes (especially when those good looking women egress from cnet.com - oops digressed). In those moments, I'm not really seeing anything (exception noted above) but my mind is just cranking on something. After a few of these sessions (the quantity varies on how complex the problem is I'm currently working on) I get the Aha! moment.
So I guess the skill is to be able to reduce conscious focus to free up access to your subconscious at opportune times. In my college days, I used to do this at inopportune moments, such as driving home. On several occasions, I would drive right by my apartment and basically start getting lost before realizing I had been in "subconscious" mode and had no idea where I was going.
An excellent way to access your subconscious is hard-core exercise. I've had the experience when swimming many laps, biking up a mountain, or cross-country skiing where I hit "the zone", the moment when your body is taking you with very little mental effort. That is when the subconscious flys and you can really solve some of the hardest problems.
I think sleep-deprivation is also a way to reduce conscious focus. I've hatched many integrations when running on too little sleep. There is the "sleeper's high" period which is especially good for subconscious work. Beware, however, of the big low you can get afterward. Push it too far, and you can get downright depressed. My record to date is 72 hours of focused work with very few breaks. I would have made it even longer if I hadn't bent over to tie my shoes after a shower - I woke up several hours later. (The good old college days.) The key to surviving the sleep deprivation lows is to work on really exciting and inspirational problems.
You might try voluntary rapid deep breathing to simulate heavy excercise. It's a very strange sensation and I wouldn't recommend doing it too often (maybe even check with a doctor first). Generally, after about 5-10 minutes, I feel very similar to the way I feel when working out, except without the sweat, elevated heart rate, and muscle strain.
It's not exactly practical to swim 20 laps then sit down and do some design or development, even if you could bring your laptop to the pool.
But yeah, metacognition techniques are basically metaprogramming for your brain.
