Persistent storage of arbitrary variables with activities?

[WJCFerguson]

Activities look really nice - they fit very well with some hacked things I already do.

But, AFAICS there isn't a facility to store arbitrary variables with an activity? Unless I missed it?

I should cycle back to my use case in case I'm asking an XY question:

One of my hacks is to associate a remote hostname with a tab as a parameter for a number of actions, and activities could do this better. I hold an alist of the remote hostname against the tab name (fragile!). Activities could do it much better with their persistence, if I could save/restore the remote hostname variable with the activity. That doesn't currently exist does it?: save/restore arbitrary variables with the activity.

A deeper thing would be to somehow hook the hostname into everything done from the activity, so e.g. any async-shell-command or find-file in the activity does so on the host, but I'm not sure there's a tidy & robust way to do that?

As a separate related issue, for some of the hosts I connect to, I would not want to persist the activity at all (in fact I'd only want to persist a small subset). I assume should do something with activities-anti-save-predicates, though again if I could associate a "don't-save-activity" variable with the activity that seems like it would be easier.