I'm not sure that a KM palette is the best choice for your task. It is going to be very difficult to automate dynamic palettes.
OTOH, using the new Prompt With List action (KM Wiki), is very easy to use. If you need more flexibility then you can consider:
- MACRO: Spotlight Search Prompt by @DanThomas.
- Custom HTML Prompt action (KM Wiki)
- There are many examples of this in the Forum.