I don't know why this has to be a once-per-year event. Why not allow federal workers submit ideas whenever they want?
The State Dept already has a robust “Sounding Board” intranet site where employees can post suggestions for improving the organization. Secretary Clinton started this in Feb 2009, and so far, people post 50-100 suggestions per month. Employees can also comment on each others’ posts, and the admins apply a label on the status of the suggestions (“done”, “in the works”, “do-it-yourself”, “not feasible”, etc). They have about 50-100 with labels (out of ~700).