Basic example of a j2c-mithril integration - http://jsfiddle.net/qe805q4q/1/

base.js

var styler = require('./styler');

function mainView() {
  return [
    styler.view(),
    //...
  ];
}

somewhere.js

var styler = require('./styler');
var m = require('mithril');

var cls = styler.attach({
  foo: {
    background: 'green'
  }
});

function someRandomView() {
  return m('span.' + cls.foo, 'Some random content');
}

styler.js

var m = require('mithril');
var j2c = require('j2c');
var styles = '';

module.exports = {
  attach: function(style) {
    var scopedStyle = j2c.scoped(style);
    styles += scopedStyle;
    return scopedStyle;
  },
  view: function() {
    return m('style', styles);
  }
};

packaged: https://github.com/StephanHoyer/mithril-j2c