Self discipline is the way to go. Ironically the more often you induce a deeper state of relaxation the more often you dip into alpha. In all probability the alpha state is what you are using when you access other conscious information. Using such techniques as photoreading / meditation / self-hypnosis the individual has more alpha brain wave activity throughout the day. The brain is shown to have all frequencies present at all times, just at different levels moment to moment.
The point is you don't need to worry if you are producing alpha /theta to or the "right" brainwave - you'll do it anyway. It's more a case of practicing the methods until they become integrated so that 'your' mind functions at its best for you to produce the results 'you' want. Finding scientific proof isn't going to make any difference to your abilities. What you put into it is that counts.
BTW scientists have proven that it is aerodynamically impossible for the bumblebee to fly. Good thing they can't tell the bumblebee that. The poor thing would have to give up flying and take public transport to work. 
