i had a similar problem with pepper (also a keen stepper upper, you almost don't have to ask) but i found a solution pretty quickly and i might come in for some criticism for it but it works for me.
when offering pepper a finger or arm for step up i put a finger under her beak and she hooks her self up without even attempting a bite whereas before i did this i almost certainly got bit, if she attempted to bite the hand i offered for her beak i held my finger up vertically and said "no bite" kind of like this
but i didn't waggle it (wayyy too tempting for a nibbler) it worked for me and now the holding a finger up and saying a firm no can pretty much curb any undesirable behavior.