I got to agree with Sain and Sketchgrad.
There are only two ways I have seen this done successfully. Ether the employee was in a directoral/partner role and oversaw designers rather than designing the nitty gritty and doing the grunt work or they were indeed interns/apprentices, helping out here and there.
I have seen specialists brought on for specific tasks and projects such as surfacing work or rendering for POP material. But they were brought on as contractors or freelancers.
Maybe in CMF something like this could work? But I doubt it.
As Sketchgrad already mentioned, not being available on a fulltime schedule will make it difficult to lead a project.
If you are only working Mon-Wed, what happens if meetings with suppliers happen on a Friday? Or client presentations are scheduled Thursday?
I would just not take this risk as an employer and I would expect that my designers are working full hours, as do all the different branches and people that designers work with in the process of bringing a product to market.