Depends on where you live. Fl and LA are a lot stricter. To use shorter nails reduces the load accepted on the hanger. What does your plan say? The Inspector will look for this, for your family's safety. You could just cut an 1/8" wider space than joist width, and bear the new ones on the house sill plate, then nail to existing joists. You would then have your solid blocking required for rotation and fire-stop.
http://www.strongtie.com/products/connectors/LUS-HUS.asp Be safe, G
http://www.strongtie.com/products/connectors/LUS-HUS.asp Be safe, G