I use a great prog called CD-Boot. It puts an additional startup-sequence in your S drawer. At boot up your Amiga first looks to see if there is a bootable CD in your drive. If so, it gives you the choice of booting into the CD or into Workbench. It makes an A4000 or A1200 act just like a CD32 8-)
It checks your CD drive at a very early stage of booting up as CD32 games usually require the full 2MB of chip ram of course
:-)
I've had it for years myself, but to see if it is still available you could contact the author Thomas Kessler. His E-mail address is/was kessler@fim.uni-erlangen.de
A4000 Mad