Org capture within current agenda item?

I know I can add a note to a currently visible agenda-item with z, I can capture to the currently clocked-in item by adjusting the template to (clock), and I know I can easily refile after capturing. But does anybody know the proper capture template to set so that I can org-capture to the currently highlighted agenda-entry in an agenda view? When I go C-0 C-c c t I get the error: "Buffer is read-only: #<buffer *Org Agenda*>".

This would allow me to set up an agenda search for my currently active projects, and allow me to easily capture ideas for projects during weekly review.