Maybe you could create a custom template for the AcyMailing content plugin. You can add this template in the settings of the content insertion plugin form AcyMailing. Here you can get the custom fields from the aticle and display it any way you want. You do need to know how to the custom field values from an article using the Joomla framework, so you might need to do some searching on how tho get that done. But I think this will work.