I'm afraid selling arms to both parties won't work in this case, since selling arms to iran is kinda a red line for countries like saudi arabia or israel, since this threaten their very existence. I also don't think Israel can help much in restraining the US from selling arm to taiwan. Sure Israel lobbyist are powerful in the US, but even they have limit. They can't cross the US national interest, and it is in the US national interest to provide support to taiwan as it is a soft spot for China, the biggest rival for the US.

Frankly, I would rather target taiwan directly. I always believe that it is possible for China to put the greatest amount of pressure on taiwan today by targetting the businesses. China should force the foreign companies in taiwan to choose between taiwan and mainland market. That will take away significant economic activity from taiwan. Just like how the US did with Cuba. Of course China also need to keep opening the market more for foreign companies to do that. As for taiwanese companies, China should offer carrot and stick to them to move their operation to mainland or at least out of taiwan. With their economy in tatters, their standard of living will decline, when poverty starting to kick in, mainland will look like a heaven to them.