Generate the files locally and then push them to the worker? Even with a JS based SSG that's the only way to do it and the difference between worker and pages. (workers have no build step)
I was under the impression that workers are just lambda functions, and therefore would fall under different billing rules than pages which serve static files (with unlimited bandwidth).
But workers apparently have a 'Static Assets' feature that just serves static assets (like pages) and comes with free unlimited requests, unlike worker function invocations, so as you say it seems to be essentially the same as pages.
What I meant the same as worker, is that under the hood, pages are just workers. The Static Assets feature was probably added because the by-request billing wouldn't make any sense for static assets.