Agent Download technique for unusual groups

[Harry Putnam <reader@newsguy.com>]

I'd like to hear about ways to do this proceedure.
Using gnus-agent for most of my reading:

I have a few groups that I read only casually and my casual reading
does not lend itself to category  based on score file.  Like scoring a
subject, author etc.  to cause those to be downloaded.  

What I'm trying currently is to set the category default to false and
list that group in that category.  That way I get the author and
subject in summary buffer and mark with %, presss `J u' 
(`gnus-agent-fetch-groups') to download them then M-g to actually get
them into the summary buffer in downloaded form.

This works but leaves a lot to be desired.  For example:  I'd like to
mark an article with something that would cause the agent to download
any messages to that thread.   A thread watch mark like some other
newsreaders have.  Yet still the category remain default false.

That is, I want a mark that causes a specific thread to be downloaded
as it comes in with no more effort than my initially marking a
specific message with %.  I don't want to have to mark each newly
arrived (no body) message as it comes in.

I can think of at least one possibliity to do this using thread based
hand scoring, but can that work with a default of false?  Are there
already existing ways to do this?

A better approach might be to just download the entire
group. (Category true) and be able to set gnus-agent-expire
differently for individual groups.  Instead of the current setup where
gnus-agent-expire settings are unilateral.  Combining that with the
ability to say what gnus-agent-expire actually expires.  Like messages
with no bodys only or similar.

In short, G p mail setting be applied to nntp/agent groups.