If you were cutting large enough holes for socket back boxes and wiring some connecting sockets, you would have enough room to use a small mirror to help fishing the cables through. There's a chance that the holes are lined up despite the blocks usually being offset and with a fair amount of overspill.
Electricians usually use a rod set/fish tape with a variety of attachments to help in this type of scenario.
Should I be using some kind of conduit and terminating all the cables at the holes? Or can I just put some large grommets on the holes and just push cables all the way through?
If you were cutting large enough holes for socket back boxes and wiring some connecting sockets, you would have enough room to use a small mirror to help fishing the cables through. There's a chance that the holes are lined up despite the blocks usually being offset and with a fair amount of overspill.
Electricians usually use a rod set/fish tape with a variety of attachments to help in this type of scenario.