When you are trading for peace you can have whatever you want on one side of the table and PT on the second side. You cannot make for example PT+Alph for PT+10g. This exploit bases on this fact.
Ask enemy for peace. Choose all his techs and gold. If he answers it is not possible, don't clear the table but ask him what is his price. Is is possible, that he will want to add sth from your side, but the engine does't allow this! Now confirn the error message and choose "We accept" - you have it all.
As example take this save and ask Freddie for peace, then apply the method above.
Ask enemy for peace. Choose all his techs and gold. If he answers it is not possible, don't clear the table but ask him what is his price. Is is possible, that he will want to add sth from your side, but the engine does't allow this! Now confirn the error message and choose "We accept" - you have it all.
As example take this save and ask Freddie for peace, then apply the method above.