The FCC Makes the rules how far a signal has to be free for a radio station. Even if you claim its not stealing, its still Dinah D’Malchusa Dina and would then fall under the same category as running a red light , blowing a Stop Sign because you are late to minyan or Disobeying zoning laws to build a yeshiva.
FYI there is something called low-power radio . Which allows very low power (Like 1 Watt broadcating) without much ado about getting a license it does not cost in the millions to get one. Several such stations operation in Brooklyn and the broadcast area is about a mile. They would give you a differnt frequency than 97.5 . perhaps one like 97.6.
Also there is digital radio which allows the 97.5 frequence to be split up into I think 5 subfrequencies without interferring with WALK