I used to have a ride that started on a big hill. There was no chance to warm up.
I prefer a gradual start for a few mins, then steady cruising, then freewheeling the last few hundred yards to cool down so I dont get sweaty when I stop.

I can stretch on the bike, stand on the pedals, push your heels down and lean forward. Its better to stretch when warm, and never to bounce into a stretch, but just hold it.

I have to eat before a ride, and really have no problem with it.