Yes there have been a few attempts but nothing that we can bring to you. Just not practical yet.
I think a DIY unit that uses a purchased pot is the go.
Whether it is an API or one of the other 990 sort of things like the JLM990 is up to you.
yeah that's a plug for Joe.
I hope we will soon have a project specifically for the JLM990 as a Mic-pre very soon.