Not exactly the same situation but I am a US citizen married to UK citizen and just received my spousal visa last week.
I'm also a freelancer, but my work is based in the US. I submitted 6mos bank statements showing my savings and the intermittent deposits from my work, 2 years US tax returns showing my self-employed earnings over the last 2 years, a letter from my accountant confirming that I'm self-employed, and a few months worth of check stubs from invoices paid to me, along with a monthly budget for us in the UK and so on. In the cover letter I explained my situation and made projections about my earnings for the year, which I used in the budget to show that we could support ourselves.
I was approved the same day that the docs arrived to the LA consulate via courier. I can't say what it was that did the trick (it probably also helped to be able to show savings, I imagine) but that's what I submitted .