Knuckle Boom Crane

I've been playing with DB's and wanted to make this crane (KBCRANE.DWG) dynamic so far so good.

Now the hard part, is there a way to have a polar stretch action linked to a rotate action? ie if I rotate the crane boom can the ram stretch and rotate to fit the rotation of the boom? At the moment I have them as 2 actions and rotate the boom then polar stretch the ram to match.

Any suggestions greatly appreciated.