If you wanna take that route (as I did)
just go into your Windows-Control Panel-System-Hardware-Device Manager and go to the opposing harddrive and disable it.
After a quick system restart.....voila! no more harddrive in your way through each OS respectively!
EDIT---You could also just open my computer, right click the opposing drive and select properties, click the hardware tab, find the opposing drive in the list of disk drives (you'll need to know the location it's configured for out of your physical setup) and select it, now click properties, under the general tab you should see a drop down tab that's titled device usage, simply select disable----EDIT
WARNING! I'm pretty sure this WILL NOT work with one physical harddrive divided into multiple partitions. I have two physical harddrives with an OS installed on each. I haven't tried it with just one harddrive, so do so at your own risk!!!