HelloGabriel,
You see that granite hunk of NI manhood in the flesh, on a regular basis. Green with envy? Me? Oh, no.
Me --> 
What you need to do is communicate to him your admiration for his talent/ appreciation of his many facets etc. etc., whilst reassuring him you're not going to be a time-wasting botherer, all without needing to utter a single word or invade his privacy:
"Drum Belly", a play he wrote, comes in handy book form.
[ www.bloomsbury.com/uk/drum-belly-9781472513731/ ]
Say he were to pass two colleagues loitering outside their workplace (fake fag break?), as one of them (you) happened to hand over said book to friend (ensuring cover angled slightly towards him), telling her: " 'Drum Belly' ...you'll like it too. Thought-provoking"...
He'd surely be intrigued. Maybe even comment in his gravelly accent (mmm). At the very least, he'd smile in gratitude that someone realises he has far more to him than just GOT? 
Worst case scenario: he gives you a very wide berth, assuming you to be unhinged and possessing the subtlety of a brick. Fair enough. You tried. And no embarrassment to him or you, or catching him at a bad moment, which is sometimes the risk in approaching actors directly!
You'll at least get an interesting play to read out of it...swings and roundabouts, eh?
Oh, go on...on behalf of the rest of us.