thats a great idea. put the tile on the spot where they are currently laying. make sure the tile's back is facing the clowns. the porcelain is too smooth for the eggs to attach.
it will **** the clowns off that there is a tile in their spot and they might miss a lay or 2 cause of the change, but they will eventually except it.
also make 2 sets of those tiles. when you pull 1 to hatch in a fry tank an then add the 2nd when you pull the tile so they have it in there tank at all times. its easier to make a removeable tile to hatch off in a different tank then it is to capture them in the tank.
also try to feed the clowns more since they are breeding. i feed mine 5 to 6 times a day. they need alot of protein and fats to produce larger and larger nests. veggies is important to.
i would wait a lay or 2 more till you try to collect. alot wont be viable cause the male is still getting used to fertilizing the eggs. soon you will have gsm coming out of your ears. hehe
also on reeds mariculture get their otohime start kit for like $50. this is used like 5 to 6 days post hatch. its better than using bbs. one less thing to culture.