Don't think there is any way of blocking off the SSD (I have a similar setup and have looked), but your issue of things saving to both drives seems odd. Are they being saved twice automatically, or are they being copied by the user? Also have you properly moved the documents folder, pictures folder, etc. to the HDD?
Here is a post that was helpful to me when installing my SSD (scroll down to the 3rd post):
http://www.overclock.net/t/1156654/seans-windows-7-install-optimization-guide-for-ssds-hdds
Here is a post that was helpful to me when installing my SSD (scroll down to the 3rd post):
http://www.overclock.net/t/1156654/seans-windows-7-install-optimization-guide-for-ssds-hdds