The missing button wouldn't be a problem, you could switch by editing the config file or using one of Launcher apps to toggle. But I don't own a H2O either so I can't give any promises.
I just glanced over the
kernel sources and it looks like hardware accelerated inversion is still a
unfixed todo, but the original workaround for the Aura should still work.
@philie: That won't help since it is a installer. All you have to do is copy the KoboRoot.tgz file into your .kobo folder and disconnect from your PC, and it should reboot and and install. Note that you have to press the light button for ~1sec to activate. If you can't get it to work, please describe exactly what steps you have done.