Don't try strictly to grapple him; set it up with strikes. Get his attention with a few feints or jabs to the face, then shoot in (and I mean shoot) for a single- or double-leg. Use the single if you're in unmatched leads, the double if you're matched. General rule of thumb: always circle to the outside of his lead foot, as if you were trying to get behind him. Makes it harder for him to use his rear weapons, and who knows, you might actually manage to take his back. If he's not wearing a gi or similar article of clothing you're going to need to modify your throws for use without a gi. Basically you're going to have to use collar-and-elbow ties, over-under, double-under, and whizzer/overhook clinches to get the throws you're looking for. This also means you're going to have to clinch with him. In the words of Jens Pulver (MMA fighter), "Bite down on your mouthpiece and wade in". Probably the best way to get into range is to work off his jab. Draw his jab then slip under it for a bodylock or clinch. Or, parry or block it, then use your defending hand to follow his hand as he retracts it, while closing the distance with footwork. You might also be able to off-ballance him or even take him down by sweeping his foot to the inside without clinching him. Basically a hands-free deashi harai: use your footwork to get him to advance, and before he can put all his weight on his lead leg, kick/sweep it towards his center. Above all, keep your guard up and keep your eyes on your opponent. It's easier to stop punches when you can see them coming. Wing Chun is genrally a close-ranged system. I would have thought that you could just wait 'til he tried to close the distance, then pre-emptively moved in and clinched with him.