You can just write it yourself. Take this normal mapping shader from the tutorial as a basis: http://www.conitec.net/shaders/shader_work4.htm

Add a third sampler that either references entSkin3 as a texture or some script BMAP via the _bmap feature.

In the pixel shader, sample your DetailMapSampler like this:
float Detail = tex2D(DetailMapSampler, InTex*8).r; // we only take the r channel, assuming it's a greyscale detail texture - *8 is the detail map scaling, try other values here

Multiply the pixel shader result/ output with Detail. This might and will darken the result a little (because 0 <= Detail <= 1), so you could multiply Detail with 1.1 or add 0.1 to it.