expiring with gnus-parameters

[Harry Putnam]

I've used "gnus-parameters" for yrs to run total-expire with specific
expiry-wait periods on certain groups... but there is always this
problem. 

Gnus wants me to actually open and close these groups before the
expiry takes place.

Some of the groups I rarely if ever have need of opening unless
just to run the expiry code.  I want to keep the backlog... just in
case I should need to use it.

I want to just let these groups move along by themselves and find some
way to trick them into thinking the group has been opened and closed
so total-expire will be run, or maybe just run code periodically (on
auto pilot) that opens and closes the groups.

Maybe there is some completely different way to do this:

Can anyone tell me how to arrange for certain groups to be opened and
closed with no human intervention and for that to be automated?

The result I'm after is to have certain groups maintain a specific
backlog of messages like 90 days worth or whatever, and to
periodically total-expire them down to the actual 90 day backlog,
without me actually doing any intervention.