New HubSpot Form System - Missing system to pass data into hidden fields

Everything about the new form system is great and has a lot of features my team would like to take advantage of but one of the biggest roadblocks is change to how we access the the embeded forms. One particular piece is the use of hidden fields to send data into our system. We use this for sending utms and other parameters that are essential to our business and cannot switch to this new system until a process or documentation around passing fields has been created.