I'll be the lone dissenter and say that yes, you can do it. However, a SW tank is not like a FW tank. Just b/c someone has done well with FW doesn't mean they can just make the leap to SW with no problems. For 2 clown fish, you're going to want to get them at the same time (or within just a couple weeks of each other to get the LR/filter used to the added bio-load), and get them SMALL. I would get true perc or false percs b/c they stay smaller than a tomato clown or some others.
There are forums specifically dedicated to nano-tanks and they are full of good articles and advice to help someone who wants to start a smaller tank.
Check out www.nano-reef.com - that's where I got a LOT of my starter info.