I finally pulled this off after a couple nights of working at it!! As this is very challenging, I thought I'd post a few tips here that may help others since I didn't find much info on it myself when I searched.
Firstly, some important things I have found that seemed to work well for me in terms of controls are:
#1. if you have a Wiimote Jacket on your wiimote, take it off before attempting to get 100% on this level. The Wiimote jacket seems to decrease your control accuracy slightly.
#2. Better yet, use the Wii Classic Controller when attempting to get 100% on this level. The joystick gives you a little tighter control which is definitely helpful when going for 100% on this level.
The first few gaps are relatively easy to get past. When you get to the 2nd corner, the trick is to accelerate into the corner, but don't tilt toward the ramp until the last second before you reach the edge of the gap. Once you get your mercury onto the ramp, you lose a bit of momentum, so it helps to wait until the last second to tilt sideways to make the blob move onto the ramp.
Also, I discovered that since I last attempted this challenge, someone has posted a replay on youtube of clearing this level with 100%. Here's a link for your convenience :)
Anyway, I hope this post will be useful to others! And of course, as with any challenge, you've just gotta keep trying.