The simplest way is that you add the programmer key into the
authorized_keys file of your instance. That will authorize the programmer to access the instance. You could create a new user for him and set the proper permissions, or add it to an existing group.
You can find a detailed guide of how to do this here
If you only want to give it access you can do something like:
cat /you/.ssh/id_rsa.pub | ssh -i pem_file.pem firstname.lastname@example.org "cat >> .ssh/authorized_keys
and then your programmer could connect to the instance doing
ssh -i programmer_key bitnami@yourip
Hope it helps.