In 2005 I had a fellow in my bike club upgrade my Chorus Ergo 8sp to 9sp. It involved replacing a cam/gear in the Ergo lever and then adding the additional cog onto the casette. The casette itself needed resized aluminum washer/spacers to except the additional gear in the same space.
He charged me about $100 for the parts and his labor. None of this would be worth the trouble if it didn't work, right? I'm in California and do lots of climbing. So I am often out of the saddle, grabbing the bars in a death grip. I rarely miss a shift going higher or lower.
Some online stores must sell a kit for this. If you've got a bike stand and a good cable cutter and some metric allen wrenches and open-end wrenches, tackle it yourself.
I think the kit my friend used was purchased from Small Parts in Oregon.
Gary