I think the Windows UEFI solution is so far the only one that I've found completely eliminates future boot entries in BIOS.
It does require having a Windows 8, or 10 installed HD or SSD disk around, but it's fairly easy to follow the guide I've quoted from earlier - thread #121. It's my experience that just deleting the entries in Clover EFI Shell does nothing to prevent them from reappearing. Others in this long thread report success just using the bcfg boot dump method and edits to the config.plist, but none of those methods held permanent fixes for me.
The Windows EasyUEFI method does however seem to create one problem which I'm still struggling to remedy which is that once you rename your BOOT folder in the EFI partition to LAUNCHER and save it in Windows EasyUEFI as a new boot option, then the cloned drives (backup drives) won't boot any longer, even when you change the priority in BIOS to their partition, they just don't boot any longer. So I'm not sure what gets written to where in the Windows scenario, but it does affect the ability to boot from a different boot drive - at least in my experience. I've tried copying the EFI from the hero boot drive to the EFI of a clone, and copied the original BOOT folder (which I did save before doing the UEFI routine) where the BOOT folder is an original - but nothing so far allows the cloned backups to boot completely, they hang on the progress bar below the Apple logo. This happens even when I have done the Windows UEFI routine on a boot drive - it boots immediately afterwards, but then won't boot once I do it to another drive, as in working with a clone to make sure it works prior to doing the routine on your hero (permanent) drive - even after changing the default boot #1 option in BIOS to it. Still stumped by this, but perhaps someone will chime in with a solution of sorts.
If having a bootable backup is not an issue, then the Windows UEFI is the best permanent solution that I've gotten to work to keep multiple BIOS entries from appearing.