We do not have any specific markup that is supposed to attach resources/terms to the AMP page. This is technically impossible to do since AMP will not execute any custom JS code.
You can try to show the Registration screen instead of the login screen. For this, you should be able to add another path to the amp-subscription or amp-access component as a workaround.
In the initialization code, there are actions (sign-in, sign-out and subscribe). You will need to add another one with a path to a registration page. You also should pass the parameters in the URL which should be identical to the subscribe action.
Here are the links to the documentation for the AMP subscription and AMP access component for reference.