Tunnelling would be the solution and the through station wouldn't need to be that wide as trains wouldn't be stopped long like a terminus. I'm sure you'll cite extra cost but what is the cost of providing a lavish terminus with all its facilities.
I suspect you'd have to go a long way down at Leeds, making connections with conventional rail less fun.
What lavish facilities do you provide at a terminus that wouldn't be at any other HS2 station?