Hi Nathan.
This can be achieved by writing a custom add-on that will handle this.
I have quickly composed an example add-on for you – https://github.com/Arsenal21/stripe-payments-enhancements/releases/tag/0.0.12. Just download .zip file and install it as a normal WP plugin.
The add-on checks if custom field and email field match. If not, it shows error and blocks form submit. Feel free to alter it per your needs.