Add Constant Contact Form Universal Code

I would like to embed a Constant Contact sign-up form. Embedding the form is easy as they provide the embed code but is there a way to manage the required Universal Code without modifying theme files? It goes before the closing </body> tag.

Here is a link to the where the Universal code is described: https://knowledgebase.constantcontact.com/articles/KnowledgeBase/18053-activating-and-installing-your-sign-up-form?ic=comm_blog&lang=en_US

The alternative is a pop-up form but that still requires the Universal Code to be added to the footer.

I’ll do whichever is the easiest. Thank you in advance for your help!