Just keep at it and be patient, whatever you do keep holding it until it stops biting. Give it 10-15 minutes a day, 2-3X a week and be patient.

I got 10 BP's about three weeks back and just now started handling them. Out of the 10 BP's only one hissed and actually struck at me. Once out of the tub she quickly calmed down. The other 9 were as calm as could be and didn't even hiss. I'll start handling them once a week and gradually move up to 2-3 sessions a week for a few months. After about a year with me I'll gradually reduce handling down to 2-1 sessions a week for 5-10 minutes to keep them tame.

This is of course a side from handling during cleanings.