Idea "Docking Collar" cvel-stage thing.

[Tacolev]

Not sure if a cvel-stage would actually be the best way or even a possible way to realize this but basically the idea is for a completely minimal vessel that is nothing more than a mass and a docking port as a hacky way of converting any old upper-stage for use as a generic dockable booster.

If we wanted to get fancy there could be flags for what texture to use and whether its male or female and so on.

 

[sputnik]

I'm not sure how that would work exactly. A CVEL payload, kept permanently attached, could have a mesh and texture for a docking collar, but wouldn't provide a docking port in and of itself.
You could, though, just add a docking port to the .cfg file of the upper stage in question. Even if it's a .dll-based vessel, such as a CVEL stage, you can add parameters via the .cfg file.