Some possibilities that come to mind, maybe using a combination of two or more of these:
- Require FB auth. Remove anonymity (to an extent) from the equation.
- Launch with a canned, relatively small number of broad compliments.
- Allow only community approved compliments. If new ones are added, block until they're approved.
- Allow submissions only until the list (without revealing the recipient's name) has been approved by multiple community members. Then lock the list allowing only up votes on existing compliments.