Enforce the rules
It's 25 feet.
That's just a few more paces away from entrances. Walking through smoke is not the worst thing in the world, but it's rude (and scientifically dangerous) to smoke in front of entrances to academic buildings. Smokers can back up a few feet; non-smokers can't get farther away from the smokers who light up too close.
The rules have been in place for years and smokers haven't seriously challenged the 25-foot limit, so they shouldn't be surprised if the rule is enforced.
It's not about rights; it's about courtesy. It's the same reason people shouldn't talk on cell phones in class, because others paid equally good money for the chance to be in class. It's the same reason people wear headphones, because others might think your music sucks.
Some people, believe it or not, go to lengths to not smoke. They think smoking is dangerous - because it is. While smokers are willing to pay the monetary and health costs, non-smokers never consented to the price and shouldn't be obligated to incur even the slight risks of walking through a group of smokers on their way to Anspach Hall or any campus building. There is the courtesy element, but the health risk justifies the fines.
Look at it another way: Banning smoking is catching on like, well, wildfire. There are certainly parents and even potential students who would pass on CMU for one of the other Michigan universities where smoking isn't as blatant.
A 2007 study of Purdue students found that they smoked far more during average school weeks than during finals, so smoking can't be necessary for achieving scholarly success or dealing with college stress.
Enforcing the 25-foot rule is cheap (the $100 fines would more than pay for whoever ends up regulating the rule) and will have non-medical benefits.
It does not hamper smokers' rights anymore than banning smoking in buildings does - there aren't very many places on campus where a smoker can't walk 25 feet to get their fix. We're not aware of any contractual obligation to allow CMU employees or students to have enough time to leisurely smoke an entire cig.
The only remaining question is who will enforce this. CMU Police currently are unable or unwilling to enforce existing campus regulations, so the onus should fall on the Office of Student Life. The OSL has experience pursuing alcohol and drug violations in the dorms, just send someone out at random intervals with a camera, and after catching someone twice, give him or her a ticket. We're sure you'll catch more than one person an hour.
Several attempts at enforcement will get the word out.
Enforcement is cheap, it will help recruitment and it will make non-smokers breathe easy. Smokers: just back off a few feet to keep those nicotine-starved pedestrians happy.
