What would it take to psyop NPCs into self custody? How much can NPCs follow instructions? How can instructions be made so simple that NPCs can follow them?
Scammers are able to walk NPCs through many relatively complicated steps. So it should be possible.
Maybe look at scammers play books and reverse engineer the scam process. Find NPCs common sticking points and how the scammers walk the NPCs through the process. The scammers use fake appeals to authority to make NPCs trust and obey them. If the app speaks authoritatively then most NPCs should listen.
Maybe the app can have big scary looking warnings and instructions to follow. "WARNING! YOUR ACCOUNT IS NOT SECURE. ACTIVATE SELF CUSTODY IMMEDIATELY. Prepare to copy your seed phrase. Enter your seed phrase to confirm."