Posted: 02/02/2014 at 11:18
The problem with pruning , as you've probably found, is that it stimulates growth, so cutting a branch back may only be a temporary solution. In some of the old orchards I used to know (mainly grubbed up now sadly) old trees were supported by large wooden props braced against the lower branches - I don't know if that's a possibility for your tree?
There's some info here http://www.ashridgetrees.co.uk/blog/remedying-a-tree-that-is-falling-over/
It also suggests pruning on the opposite side to the way the tree is leaning, thus encouraging more growth on that side to even up the weight distribution - well worth considering.
As for getting mistletoe to 'take' on your tree, info here http://www.telegraph.co.uk/gardening/howtogrow/3345933/Mistletoe-How-to-grow.html