Are we talking about your customers being given shell access and you want them to be able to connect via SSH using keys instead of passwords?
If so, yes, you just create an .ssh directory in /home/[username] and put a file called authorized_keys in it. You ro they generate a key pair, copy the public part of the key to authorized_keys and you are done.
You may need to modify the permissions on authorized_keys and indeed .ssh to make them owned by the user and read only for everybody else, depending on the distribution you use.
In fact they can do all this themselves if they have shell access. There's no need for you to get involved.
However this will mean you'll need to open port 22 to everybody, which is not a great idea. Of course if you disable password-based logins and only enable key-based logins then brute forcing passwords won't be an issue.
Faris.