index.js

var template = require('babel-template');

function getAst( t, code ) {
	// we first try to see if it's a simple stringified value
        try {
                var val = JSON.parse( code );
                return t.valueToNode( val );
        } catch( e ) {}

	// if we reached here, it's probably not a simple value but some code
        var ast = template(code)();
        return ast;
}

module.exports = function( babel ) {
    var t = babel.types;

    return {
        visitor: {
            Identifier: function( path, state ) {
                if ( t.isIdentifier( path.node ) ) {
                        if ( state.opts.hasOwnProperty( path.node.name ) ) {
                                var definition = state.opts[ path.node.name ];
                                path.replaceWith( getAst( t, definition ) );
                        }
                }
            }
        }
    };
};