I'm sourcing a few sites for my answer - puget systems has a lovely overview on their blog on the difference between chipsets and that essentially explains that the Z series has SLI support since it can split up lanes from the CPU and the other models can't.
Annoyingly, while intel's page for the b77 chipset explicitly says Supported Processor PCI Express Port Configurations: 1 x x16 the z77 specs do not mention this specification at all.
However there's a bit more to this. The board supports crossfire since crossfire is designed to work with dissimilar boards (see page 26 of your manual), which confirms what puget systems says about the chipset, as well as that you can have 1 x16 not 2 x8 as is typical for SLI.
TLDR: No, SLI is not an option for this specific chipset and board.