Could I suggest... if you already have the compact flash solution - use your PC (WINUAE) to transfer the install set to your flash card and install it from there?
Oops - sorry thats probably not an option as I neglected to notice you are wanting it for OS4.0.
I used to have a 4 way buffered IDE adapter which worked well for the CD Rom (OS3.1 though) and a slimline external CD Rom drive with the Alegro Floppy boot disk. I used it to put on 3.9 cd at the time. I don't have the IDE adapter any more but I have the CD Rom Drive and boot disk. Don't know if it would help you but if you need the drive for a loan of just to install and send back - let me know.
John
