i doubt anyone, except the loaches know the difference to be honest! If you hunt around for breeding reports on the www, you will find a few places that give supposed hints, or tips to tell the difference, but i would be suprised if any of them are accurate. They are also virtually unknown to have bred in home aquaria, hence why so little is known about sexing them i guess..
Don't forget the size these fish can reach under the right conditions.. a rough rule of thumb is fish arnt mature enough to breed (and thus sex) until they reach 1/3 to 1/2 adult size, which for clowns could be in the region 4-7".