Apparently the BIOS dead ROM and its usage is not very known to many DOS users.

This "dead ROM" contains the BIOS setup dialog routines.
Obviously these are never accessed from DOS.
So there is no reason not to (re)use this space.

Almost all standard 64kB BIOSes from somewhere in the 1990s on have their setup dialogs code in the lower BIOS area (F000-F7FF with 64kB BIOSes).
AMI started first with that. Award, Phoenix and others followed soon.

What does this mean to you?

You can add 32kB upper memory on your DOS PC with adding a simple "I=F000-F7FF" in your EMM386.EXE line.
As this is ROM area, neither Memmaker or other tools will dare to make use of that range.

Now the question is: from which version upwards of the particular BIOSes does this trick work?

Please test and post success/failure result.
Please specify your BIOS make, and date or version.

Note:
For me it worked for almost all boards I used since somewhere in the 1990s.
Even at some older 32kB BIOSes there is reusable "dead ROM". These are rare by now, but success/fail reports with these (using the range "I=F800-F9FF" or FAFF) are welcome too!

I start with the BIOSes I now have:

DFI K6BV3+ A1 (64kB Award 1998 PCI/PnP 586): Works fine!
Rhino 810S-BCE (64kB Phoenix BIOS D686 1998): Works fine!