Unified Search - Return custom field

Hi,

I am trying to show a custom field in a unified search results.  I can successfully add custom fields to the index based on extension methods:

SearchClient.Instance.Conventions.ForInstancesOf<MyContentType>().IncludeField(x => x.MyGenericExtensionMethod())

I can filter on the custom field:

mySearchClient = mySearchClient.Filter(x => x.MyGenericExtensionMethod().Match("text to match"));

... but what I can't work out how to do, is return the result of the extension method into my results.  NB: I've run out of ISearchContent fields to override / project into (primarily because we have different types of searches on the site, which require different implementations of the same field to be displayed in the results, e.g. different excerpt/summary text).  I don't really understand the CustomizeProjection method which I suspect may be the answer?  

I guess worst case I can use specific elements in the SearchAuthors field for different purposes, but it seems a horrible hack.

NB: I found Per's comments in this article useful to get so far

http://world.episerver.com/Modules/Forum/Pages/Thread.aspx?id=79729