I installed PyQt5 globally on my win7 system (python 3.3), using the installer provided from the official riverbank website.
Then i created a new –no-site-package
I faced the same issue installing PyQt5 and SIP. The solution for resolving this problem for PyQt4 as specified on Is it possible to add PyQt4/PySide packages on a Virtualenv sandbox? worked for me.
I manually created symlinks to the PyQt5 and sip.so from within the virtualenv/site-packages directory. An ugly solution but gets things working.