Any ideas how to automate this 3D operation?

[Anonymous]

NOTE:
This was originally posted in autodesk.civil3d, I'm reposting in here, just
in case there's a different group of people lurking around, or if someone
can write a utility that does this. Not necessarily looking for a freebie, I
can pay for a routine. My VBA skills are not sufficient to tackle something
like this.

Please see attached images for more detail. (can't post images, please email
for images or see autodesk.civil3d discussion group)

Here's the explanation:

The drawings I receive contain building pads (yellow linework) and streets
(cyan linework) as 3d poylines.

I need to draw a 3D polyline around each block of lots (Red line) picking
one corner of each lot (white squares).

The idea is to approximate the bottom of the lots and lose the stairstepping
effect, but still account for the elevation of each lot. I thought about
picking the first and the last lot in the block, but the difficulty I often
encounter is that lots are on curves (which alone isn't the biggest
problem), but that lots don't have equal elevation separations. They're not
always 3.5 feet vertically offset from one to the other in the block. For
some idea what the overall site looks like, please see grading block2.gif.

I keep thinking something to the effect of a GIS buffer type operation, but
in 3D. The lot elevation doesn't necessarily
have to be on the lot corner,
as long as I know where it is so I can make adjustments. Right now I do it
by hand, pick, pick pick, but as I'm picking, I keep racking my brain
thinking there's got to be a better way.
AutoCAD, LDDT or C3D or similar solution would work. Thoughts, Ideas?
Thanks!
--
Connie Barrett
Director of Data Visualizations
Pacific Soils Engineering