One problem you all seem to have is that you can't seem to separate the training methods from the application. We've established that aiki is numinous; it is not really a thing without a couple of different forces coming together, right? So what do you actually do when you wake up in the morning at the crack of dawn or when you begin your last three-hour solo training session at one in the morning?
I don't think that aiki is numinous, but that it is one concept that is made up of a number of component parts, like the famous elephant in the story of the five blind men and the pachyderm. There are different principles involved in its expression, and one can learn some basic aiki skills and express only a couple of those principles. Not the complete picture, yet still aiki.
As far as what I actually do for solo training... I always start with exercises that condition body alignment -- stacking of the joints so that there is minimal use of muscle tension to hold my body up, and certain muscles and muscle groups typically used to hold us up and to effect arm and shoulder movement (among other things), are thus relaxed and have potential energy to be utilized for other things. The potential for internal power begins with joint alignment. That's step one.