ember-cp-validations conditional validator

I'm using ember-cp-validations on models and forms. I want a validation to be active only when certain conditions are met. Like, when a route is active or when a component is used in a particular context.

To illustrate, I have a basic email model that has typical validations on the model itself. When that model is being used in the context of a user account, I want an additional validator to be active (a username-exists validator, used to tell if they are trying to update their email address to one that exists on another account).

My email model:

import DS from 'ember-data';
import { validator, buildValidations } from 'ember-cp-validations';

const { attr } = DS;

const Validations = buildValidations({
    email: {
        validators: [
            validator('presence', { presence: true, description: 'E-Mail'}),
            validator('format', {
                type: 'email'
            }),
            validator('length', {
                max: 200,
            })
        ]
    },
});

export default DS.Model.extend(Validations, {
    email: attr('string'),
    optin: attr('boolean', { defaultValue: false })
});

I already have a username-exists custom validator. I just can't figure out how to add that validation conditionally.

The simplest solution would be adding the validated with a disabled option that keeps it disabled unless a condition is met.

validator('username-available', {
    debounce: 300,
    disabled: computed.bool(what is the dependent key??)
})   

But I have no idea what the dependent key would be. I don't think the route name is available in the model definition.

Or should I add the conditional validator to the component itself? Is there a way to append a validator to the validators array from the component js?

I think I am probably missing something obvious ;)