I think the character has to be built in or using a built-in power. For built-ins, you just go to the Powers tab, and in the bottom box select 'melee: airborn targets only'.
If you can select the raptor melee power in the Hero Creator, then that will do it. If not, you might be able to copy the raptor character, use the heroeditor to change the name and mesh to the character of your choice. That might work.