WOuld the ENPA lend you a large carrier or dog cage to keep him in? Maybe a live trap with good food in it - I don't want to think about what traps the 'boss' would be using.

He might likely need neutering, which will help his wandering.

Bless Guido for what he is doing! And you for wanting to give kitty the best chance.

A live trap with food might be best. Then cover with a thick towel so it stops him being scared, if he is - he might panic.

You'll get lots more good advice!