Yeah, I don't know what I was thinking. You will probably have to use the LiveCD to fix it, as phillw said. However, once you figure out which partition your root filesystem is on, you need to mount it. For example, if it was on /dev/sda1, you would issue the following:
Of course, this is just an example. You will have to create the mount point if it doesn't exist.
sudo mount /dev/sda1 /mnt/sda1
Then, working off the example mount point, you would issue the following to change the permissions back:
sudo chmod 755 /mnt/sda1/bin