Answer:
Tom is saying they can use the picks as long as they pretend they are using case knives. At this point, there is an implicit meaning to the text. Tom knows they will never get the job down with case knives, so they have to use picks. But that reality interferes with his fantasy-inspired plan. He will give up his fantasy in favor of Huck's reality, but he will not do it without justifying his actions and clinging to the idea that his way is the "right" way to help Jim escape. In other words, he is conceding that Huck's reality-based approach is better than his self-created adventure. He just can not bring himself to directly say it out loud.
Step-by-step explanation: