A professional diagramming tool that helps users visualize complex information through easy-to-understand diagrams.
Kathy,
As Cliff said, Visio does not provide a way to show that a shape sits on top of a lane but isn't part of that lane. (I am intrigued by your description of software that provides dashed lines for this purpose. I'm curious -- what product does this?)
There is an alternative that could work because Visio supports the idea of a shape that lives on the border between two lanes. (Note that this doesn't work across an intervening lane but it's very easy to relocate swimlanes: just click and drag the header of a swimlane to move it above or below other lanes.)
For example, normally when you drag a shape into a swimlane you'll see a green line appear on all four edges of the lane:
However, if you position a shape along the border between lanes, only that border will light up:
If you can position lanes A and C to be adjacent, the location of the shape on the border will convey the idea that it's part of both lanes.
BTW, one of the sample diagrams provided with the Cross-functional flowchart template (click once on the template thumbnail to see the sample diagrams) uses this feature: