Looking at the Camcycle
site, there are more things happening. There's a cycle path from Sawston to Babraham (although I guess that many riders would prefer the road), and discussions of routes from there to Abington (from where you could use the minor road north of the A1307 to Linton).
Cyclestreets suggests that a low-quality unsurfaced path
has since been provided (note YouTube link on that page). You have to walk over the bridge, which has a significant number of steps and only a wheel channel to help with bikes. Another possibility though!
It's all better than my recent investigation into Mildenhall-Thetford, where there are no alternative roads or bridleways at all, and the Highways Agency have basically admitted that they didn't consider non-motorised traffic when plastering a near motorway all over the existing (if unpleasant) all-traffic road.