You can say words "I love you"...
But I think you can only say I love you with your behaviour.
If you really love someone, and you can let him/her know that you love him/her, what you are going to do is allowing the other person understand it in your behaviour.
When you need to say with words "I love you" you are in many cases trying to get something from it, wheter it is the other person to get happier, or trying to get a kiss, or trying to create a romantic ambience before sex or ... whatever you could want from anyone.
If you really love, you say it with your behaviour, and the other person will gradually, and in the course of time, start understanding what it means and understanding that you really love him/her.
I think that's the only way to say "I love you", but of course I also say it with words... and what I want to achieve is the other person to focus more in that fact.