I think you can achieve what you want (let the property be searchable but not return it) by setting the property store to no.
For example:
class MyDomain {
String name
String email
static searchable = {
email index:'analyzed', store:'no'
name index:'analyzed'
}
}
In this domain I say that name and email are indexed and analyzed (so they can be searched) but the email property is not being stored, so it will be null when the object is returned. For other properties check: http://grails.org/Searchable+Plugin+-+Mapping+-+Searchable+Property