I will admit I thought about using bikes for speedwork but after having worked with a couple of triathletes and the problems they have in the first 5 minutes off the bike trying to get into the running stride. The last athlete I worked with hammered the bike leg to test if a change of focus in running would work.
From where I sit, they use shoes that clip to the pedals to enable them to use both a push/pull pattern giving a more efficient/faster bike leg. I am assuming the hamstring is primilary a stabilising force and not a power force in the running mechanics.
like John I would go with one of the CF sessions and forget bikework for speed.