Zbrush tangent vector displacement maps

[Toonafish]

Hi,

Has anyone been able to get the Mental Ray vector displacement shader to 
work with tangent vector displacement maps coming from Zbrush ?

The diagnostic file tells me I should use a FlipandSwitch setting of 10, 
but that only results in chewing gum : 
https://dl.dropbox.com/u/4271217/mentalvec_tangent.jpg

I tried switching color channels in the render tree, and different 
tangent evaluation modes in Zbrush, but no cigar so far.

Thanks,

- Ronald