Wendi,
In every course that we offer using PayPal, we also urge the teachers to offer self-enrollment using an enrollment key in addition to the PayPal enrollment. When students try to enroll in the course, they are offered both routes into the course. If they are able to enter a correct enrollment key, they are not required to enter any payment information.
We do this to provide a back door for selected students. For example, a teacher may also be offering F2F workshops and wants to give those participants access to the course. Or, the teacher wants people to test the course. By giving those selected people the enrollment key, the teacher is able to give them "free" access to the course.
Simply provide both PayPal and Self-Enrollment (with enrollment key) as enrollment methods. Works great!
Larry