OK, i dont know how the EK Si cluster is setup, but with my EF Si cluster, you can remove 4 little screws in the back, and two tiny screws by the Speedometer needle. If you pop the housing open and inscrew this, you can take out just the speedometer and swap it with your stock one, without having to swap the whole gauge.
Hope it helps you out.
If it doesnt try to find a shady used car dealership and ask if they could do it for you.