Written offers must be valid to all third parties.
http://www.gnu.org/licenses/gpl-faq.en.html#WhatDoesWrittenO...
So you still need to be in possession of the binaries. it is not any 3rd party, it is any third party who has possession of the binaries.
Please read the GPL compliance guides as well, which cover this in some detail (i quoted it for you in the other comment).
What you write would be correct for GPLv3, which uses the phrase, "accompanied by a written offer ... to give anyone who possesses the object code "
This was specifically changed in the third discussion draft of GPLv3 (see http://gplv3.fsf.org/gpl3-dd3-rationale.pdf) In any case, i assure you: if you try to restrict it to people who have binaries, various parties will take you to court for non-compliance :)