OP, just a little insight from someone who has been teaching at a CC for the last few years and who has dealt with her fair share of students not dropping and then wanting their transcripts changed: When you finally talk with the instructor whose signature you need, make sure you have whatever document you need him to sign in hand.
If your school is anything like the schools I've taught for, you likely need to have the instructor sign a carbon-copy paper and write a sentence or two about why the grade should be changed/removed. Then the Dean of the department usually has to sign the paper, and then usually the Dean of Students or some other schmuck.
Also, make sure that you don't just hand your instructor the page blank. Fill in all of your shit--name, student ID, etc.--and also fill in the course information (section #, year, semester). The last thing this dude is going to want to do is sign a blank sheet or wait for you to fill in the information like a bumbling dumb-ass.
If I sound a little annoyed when talking about this, it's because I am. As an instructor, the last thing you want to do is stand in the hallway after class while an unprepared kid wastes your time by not being prepared.
Lastly, here's the good thing: the process is literally just getting signatures on paper. No one really cares about the ethics of whether or not the grade should be changed. They just hate being bothered by the paperwork.