remove the plastic scuttle tray at the back of the engine bay below the windscreen, on the drivers side next to the ECU is a bolt into the bulk head. remove the bolt (it doesn't serve any other function than filling the hole) and that should leave you a hole into the cabin underneath the dash.
I had a mate
help me out by pushing the vac hose thorugh the from the engine bay side while i was in the drivers footwell with a torch trying to find the end of it. it helps if you remove the long clip off panel below the steering wheel too.