Posted recently on the CMS FAQ site was the following question and answer:

Can EPs allow another person to register or attest for them?

Yes. Users registering or attesting on behalf of an EP must have an Identity and Access Management System (I&A) web user account (User ID/Password) and be associated to the EP’s NPI. If you are working on behalf of an EP(s) and do not have an I&A web user account, please visit https://nppes.cms.hhs.gov/NPPES/IASecurityCheck.do to create one.

For this question and dozens of other questions, please visit CMS’ Frequently Asked Questions on the EHR Incentive Program site.