Multiple parallel connectors between shapes in Visio

I have two rectangles in Visio 2016. I would like to add multiple parallel connectors between them:

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|         | <-- rectangle 1
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  |    | <------- connectors
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|         | <-- rectangle 2
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Adding one connector is easy, because I can just use the default connection points on the midpoints of the sides. But adding multiple connectors seems very difficult. I could manually add connection points using the ShapeSheet, but this seems tedious and fragile, especially if I want to have the connectors be perfectly vertical.

I've read that you can connect a connector to where it intersects with the shape, but I'm not sure where the setting for that is.

I've also read about connecting connectors to the center of the shape, but I'm not sure how to do that. The instructions say that the shape turns red, but for me the shape only turns green.