Hi Matthew
The nsis source is available together with the binary package of PSPP on sourceforge.
I am looking in the issue and hope to have an installer with the requested features tomorrow or so.
The issue is a bit more complicated as there is a 32 and a 64 bit version and it can be installed in an administrator or normal user account. So the registry settings have to comply with this.
Do you have a possibilty to check it in several environments?