Protecting hedge

Sorry but short answer to your question is no - nothing available to kill ivy that wont kill hedge and everything else in your garden.Only answer to cut and pull out ivy had similar problem with lilac ivy choking it all pulled out last year .Lilac much improved this year.

When I moved into my house 8 years ago there was a rampant large leafed ornamental ivy growing on a fence adjacent to a tall leylandii hedge on the north boundary of the garden. I stripped the ivy off the wooden fence panel to preserve the panel as long as possible. The ivy had been planted between the hedge and the fence. In defiance I am sure, the ivy grew inside the leylandii hedge and eventually started to trail from the top. It took me hours last summer to extricate it from the conifers. This year I am watching it like a hawk and removing any new ivy growth I see. I am determined it will eventually get the message :-(
I have tried carefully applying weedkiller gel just to the leaves of the ivy to kill it systemically but it hasn't made much impression on it.