how to straighten a tree

my poor 5 year old pear tree is now on lean thanks to the flipping wind 

its not uprooted and is far to well established to move so any ideas how we can try to gently push it back up right without damaging it ?

Oh dear, I had the same problem with my plum tree. There is trellis behind it so I have attached the trunk to the trellis post (anchored in a met-post) with strong nylon webbing. I have to admit I didn't push it back up gradually, just did it in one go. In fact it's happened twice, the first time I tried propping it up from underneath with a post, but the next spell of windy weather knocked that out from underneath and it fell down even further. It has stayed upright in these latest gales (I was very anxious about it  ) but the post is now being pulled over by the tree, so I am going to order some more webbing to attach the post to another post on the other side which is a bit more sturdy. It's going to look a bit messy BUT - the good news is that the tree still looks healthy with a really good crop of plums on it.
Good luck, if your pear is as obliging as my plum then the prognosis is good!