On my system you need one finger more: use Alt+Shift+Tab to scroll left in the list of tasks.
It works even with 2 fingers only:
Alt+Tab, do not release the Alt and press Left Arrow or Right Arrow to go left or right.
EDIT
After your edit I find this link. What it follow it's just an hint.
You can try to backup your XKB customization file and to do some experiments.
With the command setxkbmap -types local -print
on the system on which I am now, I obtain something similar to
xkb_keymap { xkb_keycodes { include "evdev+aliases(qwerty)" }; xkb_types { include "local" }; xkb_compat { include "complete" }; xkb_symbols { include "pc+us+il:2+inet(evdev)+terminate(ctrl_alt_bksp)" }; xkb_geometry { include "pc(pc101)" }; };
You can start with this one as your new custom file.
If it works you can modify what you need until you will find the option in conflict.