The tangent color is mostly based on rotation values. The most basic, and method of last resort is to make your tangent UV map really small, disconnect any problem triangles and rotate them until they have whatever color you're going for.
However, if you have access to 3ds max, I highly recommend this video Lavo made. Sadly he goes mute near the end but he shows how to properly save 3ds max autosmoothing data in a format that will carry over to XSI's tangents, which in many case will do a good enough job of them (though I haven't really tried specifically for cockpit like areas). If nothing else it should reduce the amount of polygons you have to rotate. https://www.youtube.com/watch?v=6VYVC0RznBA
