Rather than shopify, you can use wordpress as you will have control over full source code:
- Go to http://wordpress.org/ and download the WordPress Marketplace plugin.
- Install the plugin and activate it.
- Click on "Add New" in the marketplace menu and input the following details:
- Name: Your marketplace name
- Category: Mobile apps
- Subcategory: Apps
- Upload a .zip file of your app.
- Click on "Create My Store Now!"