sda1 ro, sda2 rw but with bindings to sda1! How to?

I try to do the following

In our fstab:

/dev/sda1                       /               ext2    defaults,noatime,ro       0       0/dev/sda2                       /mnt/dd2        ext3    defaults,noatime,rw       0       1/etc                   /mnt/dd2/binds/etc none bind 0 0/etc                   /mnt/dd2/binds/etc none bind,remount,rw 0 0

The intention is, keeping sda1 Read-Only; during the setup process we make a copy of the /etc (sda1) directory and store in in /mnt/dd2/binds/etc (sda2)

Now we still should be able to do some changes in /etc (sda1) but I want theses changes only be seen in /mnt/dd2/binds/etc (sda2)

I hope I get some help here, 'cause I'm really new with all that and my boss wants a solution!

Thanks in advance!