Nice, thanks! A few things I've done that may or may not help the response with the HM5 pads:
1. Plenty of internal damping. I went back and added a bit of acousta-stuff (fiberfill-ish) on top of my existing couple layers of damping.
2. Cutting four holes in the bottom of the pad, jergpad-style. This in particular seemed to make them less laid-back sounding and might have helped a bit with the big dip.
3. Taping the edge of the pads around where they've slid into the baffle to the rest of the headphone with electrical tape.
4. I don't use TP in front of the driver but rather some sort of fabric/felt that I got from another set of headphone pads. Can't remember which, though.
The way I see it, I couldn't get a seal with the stock pads at all. No bass, meh sound. They've definitely got some additional coloration to them with the HM5 pads, but the fact that I get a seal at all makes a huge improvement. Much of the inherent "downsides" to using the HM5 pads with the TH-02 can be minimized with the right mods, I think.