If they're already made, I'm not really sure. I know some people use super strong magnets sewn onto/in their clothing or to a support structure underneath it to hold up props like that. But they usually also embed the twin magnet in the prop during construction.
Hepzibah (with the Corsair), Scarlet Witch (with Quicksilver), Dagger (with Cloak, 2013 Ultimate editions), Mythic Cassiopeia
Chosen, In Planning:
Carmelita Fox (with Sly Cooper), Riza Hawkeye (with Roy Mustang), Red (with Subject Unknown)
Ravager, Emma Frost (with Namor, Phoenix Five editions)