If you are reselling slots in developer account, you can implement easy linking API for issued by you certificates and mobile provisioning profiles.
In this case, user does not need manually attach your certificates and provisioning profiles on device features configuration page, he just taps on "import from PROVIDER" and that's it.
You can also bundle appdb PLUS with your automatic linking requests, so this will boost sales of your certificates as well.
If you are interested in implementation of easy linking API, please refer to PDF documentation file and contact us at email@example.com
UPDATE: You can find sample import code that should be hosted on your side in attachment.
appdb easy developer certificates linking API.pdf