I also have whippets, and used to run 5 k runs with them. No more than 2 at a time, on 6 foot leashes looped so they were confined beside me. The dogs had preferred positions, inside or outside, but would settle right in and stay beside me. If I was running on a trail, they'd lunge if somethiing ran across in front of us, but otherwise ignored other people or dogs.
I always walked them out a bit first so they could do their business; once we started jogging there was no stopping for marking, etc. They seemed to enjoy it and got right down to business once we started. They were never as tired as I was when we were done (I was never very fast).
vickie