From a knee-jerk reaction, I'd say that it's not possible as it is. The final roll is to determine if the crafter has been successful on the whole process. It's not as if he concentrated for 6 months and made the item in one round.
If the cleric really wants to help the crafter, I'd allow the use of Bit of Luck only if he uses the power on the crafter exclusively for the whole process' duration. And that's not even including the +2 from Aid Another since the cleric will likely spend all his time helping the crafter.
Think it's too much? Try this instead: the crafter makes a roll with +2 and has the possibility of rolling a second time, but without this bonus.