How to add custom method to $request in Laravel 5.7?

Question

I've built an app where I have two different models with login functionality. People can either login like normal as a User or they can login as an Employer. Here's the Employer model:

<?php

namespace App;
...

class Employer extends Authenticatable implements MustVerifyEmail
{
    use Notifiable;
    use Billable;

    protected $guard = 'employer';

    /**
     * @var array
     */
    protected $fillable = [
        'email', 'password'
    ];

}

I'd like to implement the MustVerifyEmail interface but it uses some middleware called EnsureEmailIsVerified that checks if the user has a verified email.

    if (! $request->user() ||
        ($request->user() instanceof MustVerifyEmail &&
         ! $request->user()->hasVerifiedEmail())) {
       return $request->expectsJson()
            ? abort(403, 'Your email address is not verified.')
            : Redirect::route('verification.notice');
    }

I need to check if the Employer is verified with some middleware that I make. How would I implement $request->employer() so that I could get the authenticated employer instead of the authenticated user?