Complex trim problem

Complex trim problem.  Shape is so extreme I can't get split to work nor trim with surface to cut it.  I also use inventor but prefer solidworks for complex shapes like this.  In inventor I could box  in the shape and use the sculpt tool and make a solid block and then use combine tool and subtract the solid shape from my part.  But I can't find anyway to do this in solidworks.  Does anyone have a ideal?

What I would really like to do is loft around the shape I won't to cut , a lot of times when I do this,   its a box, rectangle, or triangle  shape with three or four sides and one cap,  that will extend any surface out of the solid part then I can trim it in inventor ,  but I also can't get this to work in solidworks either  if my wall have to be near 90 degrees,  at least in version 14 .  These two issues are hurting me in solidworks but there are way more positives in solidworks for this kind of stuff over Inventor.  I added a screen shot of the part, the area in red is what I am tiring to cut out.  As you can see I have a lot of areas to trim out of this part so I really need to figure this out.

Thanks JB