Why does Tom say the coffin trick would come in handy for him?

In Scene Four of "The Glass Menagerie", the protagonist, Tom, returns home after a night of drinking. He describes a magic show that he had just seen, involving a magician who had himself nailed into a coffin, and successfully escaped without removing any nails. Tom then tells his sister, Laura, that the same trick would come in handy for him, yet he contemplates how anybody could escape the coffin without removing a single nail. 

Tom's...

In Scene Four of "The Glass Menagerie", the protagonist, Tom, returns home after a night of drinking. He describes a magic show that he had just seen, involving a magician who had himself nailed into a coffin, and successfully escaped without removing any nails. Tom then tells his sister, Laura, that the same trick would come in handy for him, yet he contemplates how anybody could escape the coffin without removing a single nail. 

Tom's reaction to the coffin trick is a metaphor for his current situation. The coffin represents his life at home, where he feels suffocated and dead inside, held back from following his dreams. The nails in the coffin represent the contributing factors which trap him inside the coffin, allowing him to slowly waste away and die inside. The contributing factors include Tom's responsibility to support his mother, Amanda, and sister, Laura, by working a dead end job to pay the bills, as well as Tom's constant battle with his mother over his freedom to do as he pleases. 

In order to break free from the coffin, to save himself and live the life that he truly dreams of, Tom is forced to remove the nails that trap him inside. Essentially, Tom must remove his mother and sister from his life in order to become free. Since the coffin trick can be done without removing any nails, Tom states how the trick would come in handy for him; to be able to live a free life without removing his mother and sister from it would be a glorious, yet unrealistic, occurrence in Tom's situation.