What a bunch of muppets... the answer has been lurking on a different thread all along!
Quote Owen B:
"It’s actually at the discretion of the home team, so Luton could decide not to stream the game, and that would mean we & Sky can’t either. That’s the reason we couldn’t show Wigan domestically on Boxing Day too.
Luton might decide nearer kick-off that they want to stream afterall, so keep your eyes peeled.
And if you happen to see Sky advertising it on the red button, that’ll mean we’ve got it too. "