Upload user avatar for members addon

Hi,

How do I upload an image during the registration or profile update process in the members addon? I've added <perch:input type="image" id="avatar" /> to the reg and profile forms and also <perch:members type="image" id="avatar" label="Avatar" order="4" bucket="UserAvatars" /> in member.html. The docs suggest to specify in the form settings where images get uploaded to in standard forms, but the same settings aren't available for member forms. I can use Gravatar, but would rather offer the choice for users to upload their own images should they wish to.