Here's the thing - dual-pivots are great; I consider them essential on the front... but you don't need or even want one on the rear.

IMO, they're overkill because being so powerful, you have much less travel in which to modulate the brake. If you can lock the wheel up a hell of a lot easier, you have much less control over the brake.

But if it takes about the same amount of lever travel to lock up each brake, it makes for a nicer and more consistent feel.

So you simply get hold of some old-school single pivot rear caliper with the reverse arms, and bingo. Or just stick with the old centrepull (even these can be a bit too powerful for the rear IMO).

Get an extra-long recessed nut for the rear DP to make it a front, and upgrade the braking on another bike.