Ways to get trade power

[Diosvaporti]

Hi, Im playing as Spain and right now my main goal is to have as trade poder as possible in Genoa. I already have Napoles integrated and have Siena as vassal. The problem is that anexing Siena costs more than 700 dip points, 16 years with a diplomat taken, and all to get 3 provinces with different culture when the only thing I want is their trade power.
So the question is;
How could I get the trade power of the countries in Genoa TC, without anexing them?

 

[Kergan]

Use the Divert Trade subject interaction - it'll give you 100% of Siena's Trade Power.