Run blocked application in Windows XP

I have an old Windows XP system running inside a VirtualBox because I have some very old programs which run only in Win XP.

Now I changed my printer and wanted to install the new printer (HP Envy 6000, driver setup file) in this Win XP system.

However if I execute the setup file of the driver, Windows blocks the execution because of an unknown source (in my case in German "Unbekannter Herausgeber"). This is maybe because of a missing or old signature.

Since the system runs inside a VirtualBox without internet connection and without any security risks, I want to disable this blocking mechanism completely. At least I want to run the driver setup file.

So how can I do this?

Edit

I tried to disable driver signature checks in system settings as described here (My Computer -> Properties -> Hardware -> Driver Signing button -> Ignore) without success.

There are a few workaorunds I can think of if there is no XP installer/driver available for your printer:

• Print to a file (PS, EPS, XPS, PDF, ...) and actually print it on your host system.
• Setup a printer on your host system as network printer and access it from the XP guest system.