Today I have successfully inserted NvmExpressDxe_Small.ffs module into ROM by MMTool 4.50.0023 for my Z77E-ITX.
The result:
Download (based on latest 2.00 BIOS):
Here is the link
Congratulations and enjoy a full PCIe 3.0 x4 on your Asrock Z77E-ITX, than you for sharing the file on the forum, all the best.