Hello again -
This is a great question - a question for the ages, really. Many many people have sought to do just that and aside from Monks stashed away in the Himalayas, I have yet to meet someone who does it successfully all the time. Indeed, Tolle's book is a spiritual one, focused on meditation and other similar techniques to engage one's mind with the present (just like those aforementioned Monks).
However, I would also question why a person would like to do this? Is it because there is something holding them back or is it just that having a integrated orientation (thinking of past, present, and future) is the most adaptive way to live? To consider ourselves only in the present is not natural or evolutionarily wise for the human species. We have survived as long as we have not through strength and prowess (two things used in "the now," like a lion), but in our ability to learn from the past and project into our future. Most our our collective decisions as a race have come from our unique ability to reflect upon the past and innovate for the future. It is the reason that things like preventative medicine, solar panels, and genetic testing exist. It is the singular reason that we continue to dominate the planet at the top of the food chain, as it were.
Thus, I guess I would want to know why an individual person would want to let go of the past and forget about the future for themselves. The past, though possibly quite painful, is informative as to how and why we are the way we are. And, looking toward the future is what enables us to set goals for ourselves and achieve them. As a psychologist I often discuss a person's past with them in order to plan for their future. When we do this together it helps to reconcile the hurts of the past into achievable dreams for what is to come. This, in turn, makes the present better. SO - maybe I'm at a handicap as far as answering this question. Would you like me to open it up to others who might be more spiritually oriented?
(Again, great query!)