If you want to do this anyway you need to check the Meteor & NodeJS source code to see what the minimum requirements are to make Meteor run under PHP. The PHP stack has to interpret the commands Meteor sends and receivers, but this won’t be an easy task.
You can use comet (or reverse ajax) for realtime updates.
Trying to marry node.js with PHP doesn’t sound like a worthwhile path to go down. If someone insisted on using a system like Meteor.js, yet with a PHP back-end, it would make more sense to look at AngularJS which is mainly the client side.
Of course, that is different technology stack. If someone really insisted on the blending, one could consider using server side sockets to interact with PHP Web services; and/or use mongodb and/or mysql-node to interact with the same databases.
Comes with a backend call that will return the raw data, or a publication that stores the posts using their id’s instead of a randomly generated mongoid. And some basic templates to get you started including a Session variable that keeps track of the currently selected post.
I’m working on it a lot more and will eventually have a version that directly makes mysql calls from node so you won’t need php or WordPress; just the ability to access the mysql database (which can be remote, with the appropriate configuration, or on the same machine).