I think the best way to go is to turn up the dial on cross-strait business investment to the max. Encourage Taiwanese businesses to invest in the mainland, give them massive corporation tax breaks. Also invest in Taiwanese sectors as much as the Taiwan government will allow. Almost unilaterally confer a status of special economic zone on Taiwan. This is lay down the foundation for a reunification attempt in the 2030s or 2040s.
It's impossible; now Taiwan does not allow any form of Chinese investment. It's already quite difficult to maintain the current trade relations.