Fattus - when I initially read this I was thinking how complicated it must be for a spinner to get a simple, repeatable action, with a nice strong pivot - thinking it is so much easier being a medium pace dobber, then I re-read it and laughed (sorry) - I think what you need to do is get fit!
Reading between the lines, what I read your comment to say is... I rolled up to the net, was a bit stiff and didn't warm up properly so bowled pies, after a while I was loose and bowled well for a bit, then I got tired and my bowling went off the boil.
how about warming up before you start - bowl as much as possible to build up your stamina and think about doing some form of other mid week stamina training. I am sure Mrs Cattus would be happy to help (!)
Although I do like the meat pie idea and it is also definitely better not to think about it