Ride a zip wire between two London skyscrapers

Next September there will be a zipwire linking the Gherkin and Cheesegrater skyscrapers in the City, and people will be able to ride between the two buildings.
It’s for charity, and you need to be very fit to participate.
The fitness is because the challenge starts with a run up the 42 floors to get to the top of the Cheesegrater building (aka, Leadenhall Building), and then participants can either abseil back down the outside of the building, or ride a zip-wire over to the Gherkin (aka, 3