Just get a couple of hits from each werewolf you encounter. Don't reload with the same werewolf. I'm not sure, but when I played DF some months ago I couldn't get infected this way.
I've never really tried to get infected on purpose before, it usually just happens and sometimes I decide to go along with it, but I have tried this in a couple of different places today. It was only after doing fighter's guild quests for a few hours that I finally just started saving and reloading at this pair I've been dealing with ever since. Probability being what it is, and if the information I've read about the chance of infection is accurate, it's entirely possible that I've just had a very long string of bad luck... or would it be good luck that I've consistently failed to contract a disease from the claws of a monster? Maybe that's exactly what this is. I should find something to reduce my Luck attribute, it's sitting around 80 right now.
Spoiler I already hex edited my magic immunity away after I read that might prevent infection.
For the guard stuff, I've never had one use anything but an iron or steel weapon on me in were-form. They can't hurt you at all.