In that case you might have to set a Primary HD under the HD or Storage listings in the BIOS, separate from Boot order. Then it will give you that choice to set first in Boot Order.
However it's likely the BIOS isn't even detecting your SSD as a bootable device since you apparently installed Windows 7 to it with the other HD plugged in and it's boot files were derailed to the HD. We know this because there is no System flag on the SSD partition signifying it has its own System boot files.
The solution is to unplug all other HD's, plug HD cable into the SSD so it remains set to boot first in BIOS setup and is in the first DISK0 slot.
Now boot into Windows 7 installer or System Repair Disk
to run Startup Repair - Run 3 Separate Times
until the SSD boots on its own and holds the System Active flags.
Now you can plug back in the HD, boot it when needed using one-time BIOS boot menu key. You can remove the Windows Boot Menu if it interferes using the Edit OS Menu tab on EasyBCD (free Download at bottom of page - no name or email required)
If you don't like booting via BIOS, install EasyBCD to the primary HD OS to add the other OS on Add OS Entry tab.