Reformatting Macbook Pro Hard Drive

OK ... Here's my issue. Our 2011 Macbook Pro is one of the ones associated with the recall and fix that Apple is finally doing.

http://www.apple.com/support/macbookpro-videoissues/

When it became completely unusable last year we had to retrieve our data from the laptop so we removed the hard drive. Now that Apple is going to fix the issue, we need to re-install the hard drive. The only issue is that we have sensitive info on the drive we'd like to erase. I could do the factory reset if the laptop worked correctly. But due to the issue Apple is fixing, we will never be able to do a factory reset on the hard drive because we won't be able to see what we are doing. I have the drive in an enclosure at the moment and I'm trying desperately to find a way to reset it, but have had no luck. I cannot delete things off the drive using HFSExplorer either. Can anyone provide suggestions on how we can wipe the drive so that it can still be used on the Macbook Pro before we submit it to be repaired? ... or ... Is there another program out there that would allow me to access the mac drive via windows to delete individual items from the drive?

Any help you can provide would be greatly appreciated.