A few crazy ideas:

1. Get a sterile container beforehand, pee in that at your normal time and bring that to the lab instead of peeing there.
2. Stop drinking fluid now, go *right before* you you to bed, lay out your clothes on the floor in the order you put them on on the way to the door, get dressed while you walk to the door and drive to the lab straight away.
3. If you really can't hold it, try having half a pee in the morning, then drive to the lab where you leave the other half *while ensuring you don't eat nor drink anything until afterwards
4. Just go the the toilet at home and drink lots of fluids while driving to the lab (That one might skew the results so only do this one after everything else fails)

Also avoid from this point forward any natural [diuretica](https://en.wikipedia.org/wiki/Diuretic):

* Caffeine
* [Theanine](https://en.wikipedia.org/wiki/Theanine)
* Alcohol
* ...