The easiest way would be to simply change the specular_color, specular_value and highlight_size parameters, that'll result in highlights comparable to Poser 4's simple Phong shading. For better results, I'd recommend experimenting with the specular nodes (phong, blinn, glossy, etc) in combination with the built-in specular_color and specular_value parameters. You could e.g. plug a blinn node into the alternate_specular channel for a general smooth shininess of the skin and use a separate map in the specular_color channel to mask our more oily/shiny parts of the skin.