Firstly let me say- do. not. panic. When the mw told me at 40 weeks that it felt like his head was OP (means wrong side of head is presenting) and said it would be a 'long painful labour' I just cried and cried and panicked and then cried some more. But the truth is they CANNOT know what your labour or birth experience is going to be like; there are really no hard and fast rules and there is just no point worrying yourself about it.
At 42 weeks, I saw a consultant who scanned me and said he thought baby wasn't back-to-back...turned out he was but the point is, even the professionals can get it wrong so you might not even have a problem.
I ended up going 17 days overdue because I refused to be induced, eventually gave in to having the propess inserted and labour started that afternoon, was 8 hours active labour, 11 hours total which I consider to be short for a first baby! Head was actually quite small so as I said, there are no definites here.
I also have a friend who's had 2 back to back babies with very different labours, one much harder than the other. Yes it IS possible that the position of baby's head means you'll go overdue (as happened for me) but it isn't certain...I'm sure loads of people will come on here saying they had a b2b baby but weren't overdue.
But yes, I have heard swimming, long walks, leaning over bouncy ball can all help. I plan to spend my next pregnancy crawling around on all fours for 9 months to avoid another b2b baby 
I know I'm just waffling but hoping to make you feel a little bit better. I think it's so unhelpful when you read/hear things that tell you THIS IS WHAT YOUR LABOUR WILL BE LIKE. It will be unique to you, and your body will be able to handle it, so try to relax :)