Google "smart boot manager floppy" and download sbootmgr.dsk. You'll need a utility to create a boot floppy, I recommend rawwritewin. You can find that by google too.
Start rawwritewin and open the .dsk image. It'll write it to a floppy.
This is a bootloader only, it is not a boot disk, no drivers are needed.
Put the floppy in the drive and set the BIOS to boot from floppy. When you boot the computer you'll be presented with a choice of which drive to select, choose CD-Rom, it'll override the BIOS setting.
It even works in old 486's that did NOT have the option to boot from CD.