>Most admins probably don't get point of the secret string anyway, and asking them to put in several is just too annoying. In retrospect, I'd like to add a second layer of hashing to these, but that'd mean breaking secure trips AGAIN.

You could take the route that MrVB (I think?) did and generate the strings on first run? openssl, /dev/random, perl's random as last resort. In almost every case you are going to get a better random string than most people will supply, and if they want to change it they can. Or only have them generated if they are not supplied.

Honestly, when people care so much about anonymity they can put up with the changes required to ensure it.