Herb makes some very good points there. A certain Mike Tyson used to out-jab guys much bigger than him. Hell he even out-jabbed Larry Holmes, the Heavyweight who many believe had one of the greatest jabs in the history of the game. Herb also refers to feinting and parrying. Getting these 2 techniques working in tandem is a must to overcome the tall guys. Two vids that may help:

Feinting in boxing

Blocking a jab

You may also like to think about effective slipping combined with a short, explosive foot movement toward the opponent after the feint.

Hope this helps. If anything is unclear, I'll try to answer any questions back here.

Cheers

Fran