Display day of week (Mon, Tue, etc.) in email

Datepicker works great as an alternative to the HTML 5 default version (which isn’t supported in Firefox, IE and other browsers) — but I cant work out how to show day of week in the Contact Form 7 email.

So customer picks a date in the form on the front end, and I want the email to provide Day, mm/dd/yyyy (so for example Sat, 20/08/2016). This was working with the default Contact Form 7 HTML 5 date picker using the email tag [_format_date “D, d/m/Y”], but can’t work out how to do it with the datepicker plugin.

https://wordpress.org/plugins/contact-form-7-datepicker/