If the artist's salary is high enough, the authorities cannot ignore the request. What the authorities will surely ask is how long is the contract. I guess, an L permit is feasible: I need this person to come to CH to this job during the specific period of time. A long term permit seems a bit less feasible, how many years for the next Sistine Chapel in ZH?
There is a permit for artists. It's time-limited, IIRC 8 months or less. See here:
https://www.zh.ch/content/dam/zhweb/...ler_IW_AIG.pdf
The artist's permit is really intended to facilitate performing artists ability to travel to, and perform in, Switzerland. Think musicians, say those with a seasonal contract with a Swiss institution or venue. However, many years ago I knew a painter who was here for some months on this permit, giving workshops via an arts organization.
(I remember reading an article a few years ago, however, detailing how authorities were tightening up rules around this visa to avoid common abuses...)
Again - not the solution you are looking for, but perhaps there might be something there that could be useful in an interim context.
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Speaking of which, I see another issue beyond getting your friend permission to reside here: Establishing your business as a going concern, something the authorities are likely to be interested in when the subject of permits for non-EU employees comes up. (Remember that key to approval of a non-EU entrant is that the authorities want to make sure that this person is doing work sufficiently well paid, and sustainable, so that he or she will not end up a burden on the Swiss taxpayer.)
With that in mind, why not first start your business with your friend producing his art in his home country, selling via your gallery? The goal would be to establish credibility well in advance of trying to bring him here. Given your model is an virtual gallery, I would think you'd have a rather high hurdle to convince authorities that physical presence of the artist is necessary for the business - but a track record of steady ongoing sales in Switzerland might help.
All the best...