other than intercepting/monitoring keystrokes, not that i'm aware of. and if you were to do that you'd need to make a switch/case for different browsers (using jquery's built in browser detection) to account for how each handles the zooming/font resize. all browsers do it differently.
i had plans to research something like this as well so that i can auto zoom a page for users with poor vision (by detecting browser encoding size). for now i just use a different css sheet for now with no auto/switch. havent had the time to dig too deeply. let me know if you find a way, i'd be interested myself.