try to set your subconscious to wake you up after 5 hours of sleep. if/when you wake up, don't move a muscle. clear your mind, and relax you body completely.

SP is much easier to acheive after already being asleep for roughly 5 hours (for me anyways). your body is completely relaxed, you are closer to REM sleep than most of the rest of the night, and you should be just tired enough to fall back asleep, but alert enough to successfully maintain awareness long enough to WILD.

whether concentrating on HI, or simply the buzzing/vibrating/tingling sensation when it comes, the key phrase is PASSIVE CONCENTRATION. it cannot be explained really, one must discover its meaning.

good luck