sorry, but this really is not anything like a simple thing to do
this is all added via filters (there is no “file” you could edit) as column counts also change dynamically
you would also most likely seriously run out of space you have in that column (which is why it is added underneath to stretch across all column)

more importantly, i also cannot see why this would be an urgent requirement or indeed what would be the actual benefit of doing this
Feel free of course to make a case for it and maybe i can make this an option one day (but even then , it’s not going to happen in the immediate future I’m afraid)