I have days when I struggle to get mine in too - when i'm travelling round the country - can't always guarantee to find a loo when driving!
On these days I normally wake up early and have a litre before i leave...... i always wake up feeling thirsty on this diet anyway so i don't tend to need the loo much first thing in the morning. I then take a litre with me and drink about half of it, but space it out throughout the morning... second half i have around lunchtime. I then usually have a break for a bit and then start on third litre towards 4pm... then I only have a litre to go in the evening.. (i only have 4 litres when travelling - 5 litres when at home)
Hope this helps.. alternatively.. if the meeting is boring.. regular toilet breaks may keep u awake!!