Are you able to place custom code on the site? If you are able to add the header and footer code, DTM should work. If you are unable to add just the footer code, you might still be able to deploy it since the page bottom function is called on DOM Ready if it's isn't found on the page. With that said, DTM is considered a legacy product at this point and all new implementations are encouraged to use Launch. You can learn more on the Launch, by Adobe​ community.