You can deactivate the forcing of signed drivers by using following Settings.
Open a Command Prompt (cmd) as Administrator and type in following two commands.
bcdedit -set loadoptions DISABLE_INTEGRITY_CHECKS
bcdedit -set TESTSIGNING ON
With bcdedit you´re configurating the bootmenu of windows, so be careful. If something goes wrong you´ll need a windows dvd to repair the bootmanager.
After a restart you can install the driver normally. You just have to confirm to install the unsigned driver, just like in older versions of Windows.
Also: First post here ;)