There's no workaround that I am aware of.
We use a button edit in the form:
buttonedit f002 = formonly.file_src,required,not null,image="DownloadFolder",action=uploadfile;
and the corresponding action will be along the lines of, with some error handling of course:
on action uploadfile
call ui.Interface.frontCall("standard", "openfile", ["", %"Excel Files", "*.xlsx", %"Upload File"], file_src)
if file_src is not null then
call fgl_getfile(file_src, file_dst)
end if