No way did I miss your intention of Killing the tree.
The only way to reduce the shade would be to top the DEAD tree to about 7 ft
and grow your climber over that.
I have a 6 yr old Clematis Montana growing over a 8 ft stump that is around
7ft wide. The stump is only around 8 inches thick, the rest is the clem.
growing over itself.
I think it looks a lot better than having a few stems tied to the stem.

--
David Hill
Abacus Nurseries
www.abacus-nurseries.co.uk