Add existing remote docker engine to machine

Hi,

has anyone been able to add an already existing host running docker engine to docker-machine using the generic driver? (https://github.com/docker/machine/blob/master/docs/index.md#generic)

I want to be able to control multiple already running docker engines on Ubuntu servers from my local machine. Is there another way to create the necessary SSL certificates?

The main purpose of the Docker machine is to start and configure its own Docker Engine. Network connectivity also needs to be set up on the Docker Engine, which the pre-existing Docker Engine may not have.