The hangers would be a secure method, however they can be a pain to line up and depending the thickness of the fabric wrapped over the edges...
Buy a 1x4 (actual size is 3/4" thick x 3 1/2" wide) and split it...except instead of a straight 90 degree cut, cut it on a 45. Any circular saw or table saw can do that. Mount 1 side to wall and other to headboard, secure with construction adhesive and screws.
It will be secure, easy to remove by simply lifting headboard about an inch and projection from wall will only be 3/4", minus the fabric that wraps around, so probably about 1/2" when all is said and done...
