I've been reading some stuff about biofeedback and different brain states by Anna Wise and C Maxwell Cade.. This sensory method is making a lot of sense to me as far as inducing WILDs goes.. Wise says that alpha brainwaves are needed to bridge the conscious with the unconscious mind during any meditative state, with out that bridge, whatever happens during the altered state will be very hard to recall. She says that the most effective way to create alpha waves is by using creative imagery that involves a lot of sensory input, she then says the best way to bring theta waves into the mix is to use imagery that takes you on a journey, i.e. through doorways, over bridges, down paths, up stairways, etc.. anything where the end point is a mystery, that allows the subconscious mind to come in and create something to fill the void.. (what is: over that bridge, behind that door, beyond that path, etc..) So using a highly sensory visualisation, with the right twists and turns, done during WBTB seems to fit the ticket here, in terms of finding that edge between waking and sleeping.
(If anyone is interested, the book I'm referencing is called "The High Performance Mind: Mastering Brainwaves for Insight, Healing, and Creativity")