I think the following code can do the trick. You need to trigger it from somewhere though (haven't understand if you want it to be fired with the button or from within an app).
NSString *sbPath = @"/var/mobile/Library/Preferences/com.apple.springboard.plist";
NSMutableDictionary *sbDict = [[NSMutableDictionary alloc] initWithContentsOfFile:sbPath];
[sbDict setValue:[NSNumber numberWithBool:NO] forKey:@"silent-vibrate"];
[sbDict writeToFile:filePath atomically: YES];
notify_post("com.apple.SpringBoard/Prefs");
Haven't tried it myself, but found something like what you are looking for in the Smartvibrate tweak. This will change the settings parameter, so you should change it back to on when your application finishes.
Hope that helps!