Logic Pro 8 MIDI Autmation of plugins on Aux Channels

Please somebody put me out of my misery.

I have a mix with a large number of Aux channels and need to automate some of the plugins on them via MIDI (ie. I need to be able to 'perform' the automation using a MIDI controller in real-time).

Although editing the plugin parameters visually is no problem, I can not get Logic to pass incoming MIDI data to the plugins on Aux channels, even though I have the Aux channel strip selected in the Arrange Window.

Please can somebody shed some light?

Many thanks