You can either use mock(obj, {'x': 1, 'y': 2}) or mock(obj, 'x', 1, 'y', 2). I thought it'll be nice to provide both options, but you might be right and using just a dict of mocks is more Pythonic.
Seriously though, cool lib, thanks for it =)
mock(obj, x=1, y=2)
def __init__(self, obj, **mocks):
self.obj = obj
self.mocks = mocks
mock(obj, **{'x': 1, 'y': 2})
mock(obj, **dict([('x', 1), ('y', 2)]))
mock(obj, 'x', 1, 'y', 2).