I just did several googles, and can't find an answer to that question. Maybe you could enlighten us on the "well established solutions" (or just some google search terms to pull them up)? It seems like a serious question to me.
Currency volatility in the real world is generally considered a near-disaster-level problem. So if Bitcoin has truly solved this in a "well established" way I'm sure there are a bunch of national bank managers that would love to hear about it.
There is at least one web service that produces an average over some period. As to how you pick a good weighting, it probably depends a lot on how fast you intend to flip outgoing goods/incoming currency, or where you store value. Try terms like "VWAP", "Bitcoin average price" and so on.
I have no doubt a momentary search over on SSRN will produce a hundred papers entirely dedicated to formalizations of this process.
Once you formalize the process, how do you get people to buy into it? This seems like a typical techie thing of coming up with a mathematical solution to an issue that is really more about human psychology. When you have admittedly linkbaity websites screaming "Bitcoint has lost half of its value" all over the place, good luck explaining to people that we should really be averaging the value and everything is fine, and keep selling your goods at the current average price, etc.
This all speaks to the immense difficultly of real-world adoption of any currency that isn't backed by real government policy.
Currency volatility in the real world is generally considered a near-disaster-level problem. So if Bitcoin has truly solved this in a "well established" way I'm sure there are a bunch of national bank managers that would love to hear about it.