Well, I stumbled upon your query about configuring Yak to use a proxy server, and it brought back memories of a similar challenge I faced not too long ago. You see, I was working with a corporate client who was in the same boat - they needed Yak to play nice with their proxy server, and they needed it pronto. After some trial and error, I discovered a solution that worked like a charm:
Secure proxy. It's been my go-to for navigating proxy server woes, and it hasn't let me down yet. So, if you're still on the hunt for a fix, I'd highly recommend giving it a try.