Add this to your Custom JS:
function saveAsDraft(){
setFieldValue("Draft", true);
spjs.dffs.data.requiredFields = [];
spjs.dffs.triggerSave();
}
Then call the function from your button like this:
<input type="button" value="Save as draft" onclick="saveAsDraft();return false;">
The filed “Draft” in the saveAsDraft function is a boolean (Yes/No) field.
Please note that this will ONLY work for required fields set in DFFS and NOT for required fields set in the SharePoint list settings.
Let me know how this works out.
Alexander