passing additional options to SSH on the rsync command line?

[magicdb]

I have an account on evilserver.
evilserver requires a *login* of the form "user at domain.com".  something 
to do with cheap hosting, I suppose.

ssh gets ill on that.  ssh user at domain.com@domain.com is no good.

So I do this:

ssh -oUSER=user at domain.com domain.com

which works just fine: ssh uses the entire mess as a log in string, and 
is quite happy.

So, how can I get rsync to play ball with this ugly scheme of things?  
Is there a way?

Thanks!

PS: please cc: this address on replies, as I am not subscribed to the 
list.  thankyou very much.