You can do this using the new Distribution feature in PrePoMax 2.4.0. It takes a text (ASCII) file in the following format (for vector used to define surface traction load) as an input:
X Y Z V1 V2 V3
where X,Y,Z are the coordinates of a point and V1,V2,V3 are the components of the (surface traction load) vector in force per unit area.