If you have absolutely no control over the server, I don't see a way of doing this, as you don't control server settings, which is where this would have to be.
What you'd need to do is add this to the /etc/ssh/sshd_config file:
Now, this would effectively disable password authentication for all users, which may be undesirable. What you could do then, is put this configuration directive in a Match block, so it only applies to your user, in the same config file:
Match user yourusername
If you could get the server's admin to do this for you, it might be the way to go.
One other way is to set a really long, random and complicated password for your user, that way you're reasonably protected from random brute-force break-in attempts. Most attackers would likely be using some dictionary-based technique so as long as your password is long and random enough, it should be quite safe.
See "man sshd_config" for more details. Also, the solution I propose was suggested here.