Often we use VST FX to do a quick master audio effect and then it's not used anymore. The obvious solution is to apply the FX module to the Master audio, and use PCEs to wet-dry the signal thru the module. But too many FX modules alter the signal even if the settings are not applied, such as stereo-in mono-out. And too often bypass is not accepted as a MIDI message.
What's needed is a note event that causes a plugin to toggle its Bypass setting, as if you manually selected "Bypass" from the plugin window menu. It would even be helpful if it were a Zxx macro option (in the same vein as "MIDI CC"). Of course, a keyboard shortcut entry would also be nice...
Instead of relying on the plugin's own dry/wet parameters, have you tried using a Wet/Dry MIDI macro as described here (http://forum.openmpt.org/index.php?topic=4445.msg36524#msg36524)?
/smacks forhead
I should've searched more thoroughly before creating my similar thread.. appologies to all! <:)