data exchange with 2 web server without static IP Public

I have 2 web app in separate location (I'm planning to use meteor.js) with database on each. I want to exchange data between those 2 database when the transaction occurred on each site. But the problem is , each location only have dynamic ip public and the internet provider block VPN connection.

I also have 1 domain that hosted in internet , and the web server only provide PHP. So , I think maybe I can use the PHP as intermediate between them. Maybe I can make the system to copy the data to hosted database first and after that copy again to another site DB.

Are this solution can work ? Or maybe there is another better solution for this ? Thx