There's no out of box way to configured a pre-populated message for direct messages. If you're developing our own customization for this (via theming), you might consider posting a question to the Jive Developers space for guidance. The particular soy file is /direct_messaging/create.soy.
Otherwise, I would recommend looking into a Jive Professional Services (PS) engagement to look into the feasibility of your requirements.
Let me know if you'd like to be put in touch with our PS team.