excessive fudging

best way I've come up with to get it exact:

in rhino, draw a scaled-up rectangle that coresponds to your paper size in illustrator.

i.e. paper size is 18x24 and you want 1/16" = 1' (1:192)

1) draw a rectangle that is 3456" x 4608" (18*192x24*192)

2) place artwork to export entirely within this rectangle

3) select rectangle and artwork

4) export selected as R12 .dxf

5) open illustrator, create new document and set 18x24 paper size. close that document (this can be omitted if the last document you created was the size you want)

6) open .dxf in illustrator, and select "scale to fit art board" from the dialog.

7) delete rectangle. save as .ai