Some of the early Feigao motors had almost no magnetic 'drag'. Unlike the current designs of BL motors, those early motors did not have an iron core with the stator wires wound around it. They just had loops of wire crammed into the can with no core. So, no magnetic drag as long as there was no current flowing through the stator coils. Something like these motors:
http://www.rc-monster.com/proddetail...WAND_XL&cat=20
Of course, they also aren't sensored. Don't know if you'll find a sensored motor with no magnetic drag. If you really need sensored, then Highside20's suggestion of using a Tekin with push control is your best bet.