I know that efi variables can be read and modified in Linux via the sys pseudo-filesystem where all efivars are mounted at /sys/firmware/efi/efivars. I also know that some modified version of grub supports modifying the efi variable storage space (vss) and adds a command setup_var which can take up to two arguments, a variable identifier e.g. 0x75 and a value to write to this variable.

What I don't know is whether the efivars space and the variable storage space are actually the same thing or two different spaces. Can anybody clear me up on that?

@Fernando:
No worries, in the mean time I can answer my own question. With the setup_var command in the modified grub one can modify all settings which are stored in the "Setup-{guid}" efivar and with setup_var2 all settings which are stored in the "Config-{guid}" efivar. The first argument is actually the offset in the efivar, however you must add 4 to adjust for the efivar type header. Now that I understand this I can boot up linux on my lenovo tablet and try to unlock a few things :-)