JimR would be the best person to answer any questions for sharpening a Japanese style razor, but I hope this will help.
I believe the concept of sharpening these razors is this… you hone the flat side with several back-and-forth strokes, then flip the blade and do one or two strokes (to remove possible burrs or wire), and then return to the flat side for several more strokes… repeat until the edge is sharp. You want to keep the bevels on the concave side as small as possible, but since the flat side is one big bevel you can go to town when honing and hone for as long as it takes to get that side as flat as possible. The concave side needs only a few strokes because the bevel is small (or smaller) to begin with.
Your sharpening stone should be as flat as possible, but it’s probably best to use a diagonal strokes to efficiently use the surface of the hone (half “X” stroke?)... I suppose you could use circular strokes as well.
It is said the abrasive in Japanese natural hone brakes down as you hone (so the slurry cuts finer and finer), but Garnets in Coticules do not brake down in the same way, so your honing technique should be adjusted slightly. I would suggest you do the dilucot and/or refresh the slurry depending on the progress of the edge until it is sharp, then finish on water alone until the edge is refined, and bear in mind the ratio of strokes on each side of the blade.
As mentioned earlier don’t put any tape on the spine of the flat side because, while this will get the edge sharp, it will also change the geometry of that edge and may introduce unwanted variables… the least which, should you decide to get the flat-side, flat again… it’s just too much work.
Here is a u-tube link:
http://www.youtube.com/watch?v=1Zb_rGMWx3c
And here is a discussion on Shave Ready forum:
http://www.shaveready.com/showthread.php?t=308
Please keep us up to date.