Not sure how pianoroll velocity is related to automation? Velocity is a per note setting, not something you automate. If you want the volume of the instrument or mixer channel to change you use automation, but that's different from note velocity.
Also, using patcher sounds like an overly complicated way to automate, just rightclick on the parameter you want to automate and select "Create automation clip", or if the VST won't support rightclicking like that either use the "Browse parameters" function and right click on the parameter you want to automate there, or tweak the setting and then use the "Last tweaked" option in the menus to create the automation clip.