If those files already contain the dumped data, you can just copy them directly over using the cp command, unless not done already. If not, you can just use that command several times on one line using the semicolon, as such:
dd if=dump1.img of=/dev/sda4 bs=512 conv=noerror; dd if=dump2.img of=/dev/sda4 bs=512 conv=noerror
EDIT - This is just a rough example. It would have to be edited as needed.
It would need to be like this because using the wildcard, it would join them together as one large file.