Making a Minecraft sword from perler beads for my son's birthday cake — how do I iron it right?

So I'm about to try my hand at making something for my son for his birthday for the top of his cake with perler beads. Holy crap why are these plastic beads so God damn expensive they're just little pieces of plastic lol. So my question is, does anyone have any suggestions on how to get it right without melting them too much? I'm going to practice one first and then I'm making him a Minecraft sword to stick in the cake and pull out