I haven’t found a way to put the sidebar at the top or any different location in the mobile view than the footer. However, my thinking has changed… The footer is the last stop for the mobile scroll, so in that sense this location may be considered more eye-catching than a middle of content placement, just for example.
So I have made peace with my sidebars getting tucked under page content in the mobile view — but with one restriction, that my pages are not so long that scrollers quit before they get to the footer.