This is what my training partner and I do.
We take a slow flat ride for about 10 mins, stop and stretch for about 8 mins. We then approach the first mountain at medium pace and up we go.
When we finish the descent approx. 50 minutes later we stop and stretch again before the next mountain, which has conciderably less angle than the first as with the rest on the ride.
Sounds weird and over the top, but works well for us.
Steve.