Custom Webdriver in Appium

Hi all,

I have a following setup:
my own, custom web hosted service which implements WebDriver Protocol spec.
It communicates with the app, handles session, and so on.
I use it with wdio and works just fine.
Let’s say its url is like

I have a question, could I use it with appium? I wanted to start appium from command line and force it to use an external webdriver, but I couldn’t see such an option.
Also I couldn’t been able to understand how to do it referring to

I also could take an option where I have a separate process locally proxying requests to

Do you think there is any way?
What are your thoughts on this?

Thanks, cheers!