The humane society thing may be a dead end.
I got an EMail not long ago from a guy who does uniformed armed humane society work under these exact circumstances; he even goes along on drug raids to deal with the inevitable four-legged issues and helps with the rest of the search warrant serve. He's a former cop, but didn't retire on that status...and you guessed it, was having issues dealing with scoring CCW.
See, "peace officer status" is NO guarantee of CCW!!! People think it is, but it isn't. It's STILL discretionary on the part of sheriffs/chiefs, unless we're talking about a PAID cop/deputy for said chiefs/sheriffs.
Example: BART is a multi-county "light rail/subway" system in San Francisco, San Mateo, Alameda, Contra Costa and very soon Santa Clara. Their transit PD system is a specially chartered form of "state police", a bit like a mini-CHP. Their paid officers have off-duty carry rights but if they have reservists (dunno if they do) such folks not only wouldn't have off-duty CCW, they'd have to apply to the sheriff/chief where they live just like anybody else, and would probably get screwed...'specially in SF.
It gets worse. In the CCW penal codes, the four-year permit is specifically linked to lists of various TYPES of peace officers, including oddballs like tribal reservation police, harbor patrols, etc. Humane Society peace officers ain't on the list.
Finally, a sheriff can issue statewide only to their OWN deputies of any description (peace officer or not).
So...unless somebody can cite to codes that show otherwise, I don't think this will work.
--------------------------------
Carnitas' ideas at the bottom of page 10 are quite good, esp. #2 where positive defensive incidents are reported. #1 (quick reporting to issuing agency of problems) would have to be phrased carefully to avoid the appearance of "cover-up attempt" but that's managable. These could be part of the "deputization agreement form" (one to two pages tops, that).
