External HDD slowing down POST considerably

So this is a relatively straightforward issue, that I have no idea how to solve. I have an external HDD (Seagate FreeAgent 1.5TB) that is constantly connected to my PC through USB 3.0. The disk uses an independent power source and goes to sleep after idling for a bit. Naturally, when the PC is off, so is the disk. The problem is that whenever I turn the PC on, I also have to wait for the disk to "wake up" for the POST to complete, which wasn't much of a problem in the past, but ever since I got my SSD, it pretty much doubles my boot time.

I've heard about "quick boot" bios settings which disable a bunch of power-on tests, but my mobo's latest BIOS doesn't seem to include such an option (ASRock extreme3 890gx). Do I have any options apart from keeping the disk unplugged when it's not in use?

And it probably always will, I find the same with my Win7 computer but am averse to unplugging the 3 HDDs just for the several seconds to half a minute additional boot time as my drive letters would probably change causing more grief than I need.

It usually is because the BIOS is searching the drives for any boot files that may be on them, unplugging the drive prevents that. Have seen it happen when a CD or DVD is left in an ODD.

@Berton: Do they change letters even after assigning drive letter in Disk Management? Mine do stay same - 2 usb sticks/2 usb HDD and 1 E-Sata HDD all keep drive letters same.

I have seen a couple get changed but it probably was because of the card reader in the computer but could have been because I plugged them into a different USB port from the first time, got identified differently. Once I assigned different drive letters to the slots on the card reader I've had no problem with those, they never get unplugged.

One thing I have to keep in mind, the NAS HDD on my Router is automatically lettered as Z:, if I were to add more the lettering would work back up the alphabet from there. Because of that any computer connected to the Router sees it the same.