Yes that would work. It would be very slow though. Just make sure you create an assign for the name of the CD to your FTP mounted drive. For example, if your CD's volume name was "AmigaOS3.5" and your FTP mounted drive was "FTP" then type the following in to a shell before running the installer:
1.>assign amigaos3.5: ftp:
This will make sure the installer can find the files it needs if it references the CD by volume name.
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moto