How can I manipulate forms generated by point attractors in the "z" axis?

Hello All,

I'm new to this program and have deiced to use it for my graduate thesis.  Having said that here is the issue:

I using point attractors to generate form about a rectangular grid.  Then I'm using an extrude command to give the rectangles volume.  However, this is where my problem begins.  I would like to take the produced volumes and manipulate them in the "z" axis.  For example, I would like to be able to draw a line though the generated rectangles and have them displace (think of it as a tunnel through a hillside). 

I would greatly appreciate some insight with regards to solving this issue?  I'm sure this has been asked previously I just can't seem to place my finger on a posting.

I've provided the rhino and grasshopper files for review.

Thanks!