I came up with this drill a little while back, and had our students at the dojo playing with it last week, where you set a datum (reference point) with one hand, strike to it with your elbow, then use it to "stick" to the opponent as they bob under and out, maintaining your datum to strike over the top, then stepping into a gedan-barai takedown. It's essentially like the elbow strike from Naihanchi Shodan and the juji-tsuki/gedan-barai from Suparinpei put together. In the video, I go over a basic patner drill for it, followed by a basic padwork drill that was focused on maintaining contact with your partner's neck/head. You can do the same thing just touching the pads, though, if you want more room for your power strikes. A fun way I had folks work into this on Saturday was having the padholder throw a wild flurry of "punches" with the pads (your typical untrained flailing) so the striker had to cover up and follow one of the strikes into a grapple.
Conveniently, Iain just posted a video, today, of a drill that also makes use of datum setting and tactile sensitivity, so I figure I might as well throw it in, too!