Just a connector that can be used as a spacer in between two boards. This way tall shields don't have to be pushed up to the top of the stack, they can be in the middle somewhere. And for really really tall shields, two (or more) connectors can be stacked on top of each other.

A riser connector would be great. We would have to find an easy way to space out the connectors for the heights that we want.

Interesting idea! An itty-bitty PCB with connectors on both sides. It could also come with matching mounting hole spacers.