Try not to do all the work. Give him a window of oppurtunity and let him try - with you assisting.
At the function when he moves to the food table / drinks table - move there and as you're both pouring yourself some grub / drink - ask him if he can pass you something. When he does, thank him, smile, and do the oldest trick in the book: "I think we've met before?"
That's about it - let him take it from there. He's gotta meet you on the bridge half way.
At which point he'll say "yeah, i think i've seen you at the park." the convo can go on:
you: "Yeah, I really like that park. It's on my way to XYZ"
and then talk about XYZ a little and let him ask you questions about it.
The image of you talking to him, will boost up his confidence and after that, take the train where you will