There is still one way besides using F8 at every startup, I haven't tried it myself but should work.
So this will require the use of some tools from the Windows Driver Kit, which you can get free of charge from Microsoft Connect. First you'll use makecert to generate a test signature that you'll embed in the program/driver you want to use. Then you'll follow the directions in the first section here to use signtool to embed the test signature you just created in the driver file (or program which includes a driver).
Then to enable test signing mode, you have to run "bcdedit /set testsigning on" from a command prompt; this will allow test-signed drivers to load.
It's a very roundabout way to get unsigned drivers to load (plus you have to do it for each individual driver that you want to load), but it did work for me (for the driver that the A64Info program uses). Sure, it would be more ideal (from a security standpoint) not to need to load unsigned drivers in the first place, but that isn't always realistic...
Edit: Forgot to mention that enabling test signing mode will plaster "Test Mode" text at all corners of your desktop, along with the Windows version (on all monitors if you have more than one). As far as I know, that's just something you'll have to live with while using this workaround. It's less annoying than having to press F8 at every boot or selectively not installing the performance/reliability packs anyway