How can I associate an incoming transformation with a specific upload-mapping?

Cloudinary allows you to set up a dedicated upload-preset to be used by the upload-mapping mechanism.

That way, every time an image is lazily uploaded by the upload-mapping mechanism, it will also be applied with the associated upload-preset configuration.

All you have to do is, within your account upload settings page, name the upload-preset with the corresponding name of the mapped directory. For example: