Modify incoming Query for customfield Search

I am creating an internal plugin for Customfields and I have hit a bit of a choke point that I can not find any doco on.
I have a customfield of places that have an associated ID. Due to naming changes for whatever reason I am storing the ID against the issue using the standard Java API for that and displaying the Text name pulled from my own AO table.
However I want to be able to allow users to use the issue navigator to search using the a String name not the ID. So far everything I have tried in the CF searcher module I have done using Exact Text searcher fails to allow me to modify or return the right issue types.
Any doco you can point out would be greatly appreciated as it looks like I will have to do a JQL function which is a bit tacky.