Timely question as we had the same dilemma this weekend. We had South Beach dieters and no salters for dinner, and I wanted to do some beer can chickens. I simply left the salt and sugar out of my standard red rub, and went heavier on the other spices ( cumin, granulated onion and garlic, oregano, and some hot pepper) No one had any complaints.
Also, there was a thread here a while back about room for beer can chickens on a Weber 22 ½ kettle. I simply put the rotisserie ring on the grill. Worked perfectly. Using briquettes and a couple of chunks of apple wood the temperature averaged 350 and it took an hour and 20 minutes for two chickens.