Hi Mindset, you could use the Transform > Deform > Flow command in MoI to apply a heightmap over an existing surface.

Draw a plane at the z = 0 level of the heightmap, then select the heightmap to be the object to deform, run Transform > Deform > Flow, then when it asks for the base surface select your z = 0 plane, and for the target surface select the existing surface.

There's more information about Flow here:
http://moi3d.com/3.0/docs/moi_command_reference8.htm#flow

- Michael