Add connection point to a dynamic connector

[John]

Hi there,

Can anyone tell me how I should go about adding a connection point to a
(curved) dynamic connector? I'd like to drop another shape onto the mid
point of the connector to describe the conection relationship (ie a red dot,
or a green dot etc.).

I can't work out how to build a formula for the connection point that will
always point to the centre of the line.

Any clues?

Thanks

John