I've found a way to disable it! (workaround) By accident lol
Solution:
Install 3dmark06 (1901), and run it. After loading the first test (proxicon) press esc to stop the test. Voila! It's disabled now until your next restart. (rest of metro still works)
EDIT: Turns out timing is important, so may not work on first try.
Here's what worked for me:
Close any open programs. Run 3dmark06, wait for it to scan, load first test, then once you the fps counter is fully visible press the windows key (it'll load metro). Then WAIT for a couple of seconds (3 worked for me 5 out of 5) and press the windows key
again. Avoid any other interaction with the pc in the process.
Now it should show "error 3d device lost" or something and now the hover menu shouldn't appear when moving the mouse to the left bottom :) played starcraft for an hour afterwards, no more accidental alt tabs :)
Pressing windows + p and switching to another monitor setup will reset it.
If hover menu still appears, just click run again, and try 5 sec waiting time after the first windows key press.
My setup: lenovo x200 tablet, w8 dev x64, 4gb, external monitor hooked up with gtx550 via optimus (driver 275.something, latest available), using only external display