Try the SPH Dataset Interpolator. This will interpolate the point data onto the surface according to an interpolation kernel you can set. To use it, select your point source, then add the SPH Dataset Interpolator. In the dialog that pops up, leave the Input to the selected point source, then click on the Source input port on the left. On the right, choose the STL. Click OK and apply. Play with the Spatial Step to adjust how the point data is “splatted” onto the STL (bigger values make a bigger splat). HTH.