Restrict a custom field to only certain memberships

It would be nice to have the ability to have specific custom fields set up for different member sign-up forms. Currently, there is one sign up form for all memberships. However, I have a specific membership for students, in which I would like to have a custom field or two specific to this registration process that I would like to be required. With the current setup, I have to add it to the regular sign-up form to display for everyone and cannot make it a required field.