Not sure how many people are using this on the Kobo Aura (non-HD version), but since I picked up a refurbished unit for pocket-lint prices I thought I'd play with it. Happy to report the screensaver works fine in scanline mode, using the latest firmware.
Note: The effective screen resolution, despite being reported as 758 x 1024 pixels, is actually 758 x 1014. Anything taller that in your image will be cut off/covered by the lower-edge floating black border in the surface material.
Code:
# Values below for Kobo Aura English in 3.19.5761 firmware:
# Effective screen resolution is 758 wide x 1014 high
offset=123
standby=64dd3f2ff0891ae756a42888fdba45c7
poweroff=08406112b6212bdb54724aff4bd00b2c