If the idea seems viable I'll put it in my personal Kanban board (in a "Waiting" swim-lane). This Kanban board is a project level queue - one card per project.

If my "Active Projects" kanban swim lane has some space, I'll pull from the "Waiting" swim-lane.

This way I can schedule those ideas, if I have some time (shown by the swim-lanes on the Kanban Board)