you do not need the the Version 2 installer, but you do need the Version 2 serial number written on the box (or the leaflet inside the box).
What you can do, is contact Apple with a proof of purchase and ask for a replacement serial number, see these links as to what is considered to be a proof of purchase:
Pro Application Replacement Serial Numbers: http://support.apple.com/kb/HT1861
Troubleshooting Professional Application Serial Numbers:
Or just live with iPhoto, or buy a fresh copy sometime? I'm obviously in no tearing rush, but it would be nice ...
Aperture now can work with iPhoto Libraries, so any work you do in iPhoto while waiting for Aperture 4 will not be lost. Aperture 4 is overdue, so I would not recommend this to be a good time to buy Aperture 3 a second time