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Some breeders have had good luck with using a small flower pot. The clowns like the security of it and they will spawn in there. It is tough once they choose their spot, but as jgraz mentioned a tile would work well too.
Do you have a sump or another area you could take the water from that would not drop the water level?
How about maybe just leaning a piece of clear acrylic (plexiglass) in the location they spawn? Then, before the water change, just rotate the sheet sideways so the spawn is lower in the water.