I think we got a minor breakthrough - which we really needed as every time I so much as think about training Zac seems to have a minor relapse and we have to postpone, this is the first time I've actually tried to break new ground with limp in over a week. It isn't a breakthrough by shaping though, just what felt right at the time.
Zac would lift a paw on the cue "limp" and we had built up a millisecond of duration using the "finish" cue. Today after a little revision of the above I ditched the clicker and when he raised the paw I presented a treat (well it's just his kibble but it's working at the moment), if he lowered the paw I took the treat away, if he kept the paw up he got the treat. He got the idea super fast, now he holds the paw up and chomps treats down as fast as he can. I thought I better quit before I over fed him but maybe, just maybe, if we take our time, I'll be able to lure him forward with his paw up because he knows the treat is taken away if he puts his paw down... here's hoping anyway