Need to remove CD-ROM from Virtual machine permanently

Hi, I created a Virtual Appliance based on RedHat and developed it as OVA file witch you can deploy it on ESXi or vCenter, i need to prohibit my customers from booting this virtual appliance via Live Linux CD/DVD, So i deleted the CD-ROM of this virtual machine but the problem is a customers can add CD-ROM again to the virtual machine after deployed it on its own environment,im looking for a way to delete CD-ROM permanently from a virtual machine, please help me