FOIA request for full NSF awards proposal and report
The name of the requester does not remain confidential.

A friend of mine was recently on the other end.  NSF contacted him to tell him that an FOIA request had been made for a copy of his proposal, told him the name of the requester, and asked whether the proposal contained any sensitive information that he wished to have redacted.  

The general feeling was that making such a request, rather than contacting the PI directly, was unprofessional and borderline creepy.  I second JeffE's comment: Ask the PI first.