I just found a way to do it on a Mac though. In the Reminders app, create a new list called Email Reminders. Then simply drag that email message to that list, and set the reminder date and time (or any of the other options). Unfortunately there isn't a way (that I know of) to drag an email into another app on the phone, but maybe it could be done on an iPad (I don't have one to test with).
If you can do it on another device, it will be visible and available on the phone.