<<Do you mean so that when the part gets stitched in to the new mesh, there are no extra triangles added?
IE that all of the boundary vertices of the part will 'snap' to vertices on the target surface?>>
Exactly this, RMS.
Snap vertices part boundary to the target surface vertices, avoiding to creating triangles (or at least minimizing them) and try to keep the edge loops flow.
Or (maybe better) connect vertices from part boundary to vertices from target using JUST ONE edge
(triangulate MM method make this connection using TWO or even THREE edge, which generates the triangles).
<<I'm not sure I understand why you would want to automatically find a boundary with the same number of vertices.
In most cases, it seems likely that this would require a weird-shaped boundary...>>
As i said at another post, this would allow the user to design how the meshes would be mixed,
and not just get "randomic" triangles at green region, broken edge loop flow and increase the time he will get to retopologize that area.
<<(do you have specific examples you could show me?)>>
I recorded a video at wings, showing how i can mix a cylinder with a segmented cube.
The most important arent the commands used to do this.
The focus is: the selected area at cube has the cylinder basis same number of vertices, and this allow a perfect connection between both meshes, without generate any triangle.
Take a look at video, please.http://www.youtube.com/watch?v=_LjcbI9evYk