How do you create an approve and reject button within Email Notifications?

I have followed the instructions in the article and have been able to successfully create an "Approve" button.  

My "Reject" button has slightly different requirements.  If a user clicks the "Reject" button, it should populate the "Approvals" field with "Rejected", and require the user to fill in "Rejection Comments" before saving the form.  The button has the issue that the form is saved as "Rejected", before the user can submit comments. 

Is there a way to require "Rejection Comments", before the form is saved, when the "Reject" button is clicked?

Thank you!