You cannot have two drives visible during the Windows 7 install.
For my 2012 MBP15, I have my original 500 GB hard drive and the 80 GB SSD in the opti drive bay.
This is what I did to get it installed and I have installed on both drives, opti and hdd bay.
I had Win7 installed to the HDD but I dumped that and installed again to the SDD, I like the speed.
1) Create a working BOOTABLE Installation flash drive of Windows 7 (if you don't know what this is, google it to find out how to create one)
2) Decide which drive you want to install windows too
3) From Mac OS X, Plug in the flash drive with the Win7 installer on it
4) Run Boot Camp and start the installation
5) After partition OS X will reboot automatically, do not let it reboot, when the screen goes dark, hold the power button to turn off the machine, do not start the Win7 installer
6) Unplug the flash drive and all cables
7) Take off the back cover of the MBP and disconnect the ribbon to the drive that Windows is NOT being installed to
8) Put a piece of paper between the ribbon and the connector on the logic board so it does not make a contact. This will define the drive as drive0 for the install process.
9) Put the back cover on but do NOT screw it closed
10) Plug the flash drive back in and power cable
11) Boot the computer holding down the OPTION key
12) Select the flash drive, it is orange in color, NOT Macintosh HD or Recovery HD
13) Windows 7 installer starts... format the BOOTCAMP partiton... and install windows to that just formatted partition
14) The Win7 install may reboot once or twice do not do anything, let it do its thing
15) When Win7 is installed, running windows, desktop and programs can be ran, shut down the computer *you cannot install the apple drivers just yet, be patient*
16) Unplug all cables and the flash drive
17) Take cover off and reattach the ribbon you disconnected earlier, you dont need the paper either
18) Screw down the cover
19) Reconnect the power cable and start up the computer, holding OPTION, and boot to Mac OS X
20) Take a 2GB flash drive, formatted in Disk Utility using FAT
21) Run Boot Camp, download the latest drivers from Apple, save it to the external drive which is the 2GB flash drive
22) You will need to install an utility to allow Mac OS X to be able to write to NTFS partitions. Google it to find a couple of shareware/trial utilities, don't buy it as you will only use it once. *There is a terminal command but it is unreliable and could cause data loss*
23) After installing the utility, copy the folder WindowsSupport to the Windows 7 hard drive, it should be called Untitled by default. If you copy it directly to there, the folder will be located at the root of C:
24) Install the utility, not needed anymore
25) Restart you machine, hold Option and boot to Windows
26) Go to the WindowsSupport folder and start the driver installation *I did not have any issues with unrecognized drivers after the complete driver install. It complained once during the install but after the reboot I checked Devices and all are ok, no exclamation marks for unknown hardware*
I rarely post here, so if you have any questions I'm sorry in advance when I don't reply.