Wanted: AutoLISP routine to snap line vertices to nearest point on a polyline

I am looking for an AutoLISP routine for use in AutoCAD 2007. The routine needs to:
-- Look through an entire drawing, including inside of block
definitions -- Find all lines on a given layer -- Move (snap) the vertices of said line to the nearest vertex of a polyline on a different layer
So, basically, said routine needs to go through an entire drawing, including looking inside block definitions... find all lines on a layer of a given name, say "GUIDE_LINES"... snap the vertices of these lines to the nearest vertex of a polyline on a different layer, say "MAIN_SHAPE".
Basically, the reasoning behind this is that we have some external software that we need to feed the resulting DXF... said software needs to have the points of our "GUIDE_LINES" layer matched exactly to points of the polyline shapes on our "MAIN_SHAPE" layer (those aren't the final layer names, but just for example).
Hope this makes sense. Would be willing to purchase a pre-existing tool or pay a sensible fee to anyone willing to provide such a script.
Pretty urgent, so would appreciate any responses.
Many thanks in advance!
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