Can’t see any obvious gromet cover a hole to poke the cables through.
Had a look at the shimano manuals, but they just give an exploded view, not a “how to”.

How’d you do it? Before I end up take apart completely apart…

Well if no-one knows, this might be useful to others..
http://www.parktool.com/repair/readhowto.asp?id=117
(3rd section down)

You have to remove the top cover of each lever to expose the cable fixing and cable nipple. Then I just poked around to release the cable nipple from the mech.

Then just shove the new cable in, etc.

You may also know that the covers on the left and right-hand levers are NOT the same.

🙂

Solo.