Well... it's certainly possible, but it's mostly a manual process. Visio provides the ability to snap to isometric shape extensions. Here's an excerpt from Visio 2003 Help:
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Shape extensions appear as faint lines on the drawing page. The drawing tool snaps to and follows a shape extension. A shape can have multiple shape extensions.
1.. On the Tools menu, click Snap & Glue.
2.. Click the General tab, and under Currently active, select the Drawing aids check box.
3.. Under Snap to, select the Shape extensions check box.
4.. Click the Advanced tab, and under Shape extension options, select the shape extension check boxes that you want.
5.. Click OK.
6.. While using a drawing tool, move the tool toward or along the shape to see a shape extension.
Shape extensions work with these drawing tools:
a.. Line tool
b.. Arc tool
c.. Freeform tool
d.. Pencil tool
e.. Ellipse tool
f.. Rectangle tool
g.. Connector tool
