Unless you are actually accepted and enrolled in a BSN program you can't put it on your resume. However, as others have stated if you are enrolled in a BSN program and have an anticipated completion date that is fine.
Bachelors of Science in Nursing
Currently Enrolled, Anticipated completion May 2014
Would be fine.
Just say you are currently enrolled in a BSN completion program and anticipate completion in x month of x year in a cover letter. Not really much to say there.