I have been doing this on twitter already, and I include Karl in there too.
Vivek has said this before:
Well, I think it is time to think of ourselves as the irritant now. We did it to help keep the team/get an arena, now it is time to get a new coach. Everyone on twitter needs to tweet or retweet Vivek and Pete about getting Karl in as coach. Put reasons down: losing the players, losing the fans, season ticket holders not renewing, losing games, no reason to fire Malone, Karl's past accomplishments and desire to coach here, etc., etc. I would use whatever appeals to you personally, so it isn't the same canned stuff over and over. I retweet folks like Breton and well. And be respectful.
Obviously the folks at games with signs and chants are awesome, in a very public and positive way. But for those of us who don't attend many games, this is something we can do to help. Let them know how you feel.