I'm afraid I might be partially responsible for the lack of this work-around. In a phone conversation with the Browser Isolation product manager a few weeks before the product launch in March (but remember, well over a year after I first contacted Cloudflare about accessibility in this product), I articulated some version of the problems with a remote screen reader that I laid out in [1]. But I may not have emphasized enough that this would be better than nothing. Since it was a phone conversation and not an email exchange, I unfortunately have no record of what I said. Still, I can't take full responsibility for the fact that, to all outward appearances, they have done nothing about this problem so far.
[1]: https://news.ycombinator.com/item?id=28028682