Generating a cutting line from a Gerber outline
Newer versions of Altium have this feature.

Use the menu path Design &gt;&gt; Board Shape &gt;&gt; Create Primitives from Board Shape.

In the resulting dialog, select the check-box for "Route Tool Outline".



("Route Tool Path" in the drop-down is just a name I gave to one of my mechanical layers)

Of course if you want to have break-away tabs or mouse bites or something, you then have to edit the generated objects to create those features.