You can fake sub-surf effect in Terragen messing with translucency depending on the size of the model. Might have to be higher than 1 and given a tint.
Example gray sphere with translucency 3 tint orange yellow. In this case translucency controlled by same fractal that drives displacement (not really necessary)
*added a monolith for background and shadow examples - same translucency and sun light set to 5 in all