your idea is good actually but in my opinion if we introduce an investment or trading activity to someone who is already "addicted" to gambling it will not be as easy as you think.
someone who is already at the stage of gambling addiction they can no longer think properly and cannot limit their desire to continue gambling and spend their wealth.
there are various factors that in my opinion are not suitable if it is done by a gambling addict regarding their mindset and their habits, so it is certain that it will be difficult to talk about investment matters.
chances are your idea is good if that person has finished or has gone through therapy or treatment from gambling addiction.