1. I am "that guy", but who cares? It's like a carpenter bringing his own tools. I bought a second one after 1 year of lugging it around, because it's worth it to me.
2. Use/buy US QWERTY on everything, with US-International dead keys. I've been typing German (QWERTZ) this way for >10 years now, and it makes some programming tasks/tools easier to use.
3. Alternatively get a set of blank keycaps for your keyboard. This is actually a key ;-) feature of mechanical keyboards, you can get keycaps in all shapes and sizes and even custom printed ones. I use blanks or US QWERTY.
4. Keep a second (regular) keyboard plugged in case a coworker comes around. This is easy, as there is usually one on the desk already.
5. Borrow keyboards from friends for 2 weeks and try them out full-time. Some that I've tried were downright painful. I know it's hard to return stuff in Europe but if you can, try to.
6. Although expensive I think it's a good investment, especially if may prevent health issues in the future. Some employers may even pay for it, or offer an alternative.