Write methods for ggplot without importing ggplot2?

I'm including a ggplot.my_class in my package, and I'm basically looking for a way to do what's done in Write S3 methods for generics from other packages without importing that package? but for ggplot.
I want to do this just to avoid adding ggplot2 under depends in the DESCRIPTION file, which is supposed to be a bad practice.


ok, I think it was a dumb question. ggplot is s3, the insides are not....