I often use the aruch hashulchan’s heter when using the less holy book (as a tashmish) for the more holy one for example:
I will often put a sefer that is not kisvei kodesh down on top of a stack of papers with pesukim to keep them from blowing away. I also use large secular books to hold yerios open while I write. I still don’t get why some people think this is wrong. If the halacha was to avoid ever putting anything on top of kisvei kodesh, how could we ever cover a sefer torah between aliyos?