DV maestro Adam Wilt of ProVideoCoalition's Camera Log shared his utility on the SF Cutters list:
Question: "Once the P2 files are imported into FCP, is there a way to quickly delete the original P2 files (.mvx, or whatever they are) without having to unlock each one individually?"
Answer: "I have an Applescript droplet called 'P2Purge' designed expressly for this: it'll unlock and erase the file hierarchy on a P2 card (leaving the folder structure and an empty LASTCLIP.TXT file), then eject it. It can also be set up to allow folder purging for on-disk copies of P2 cards.
Use at your own risk: no warranty of fitness or suitability; professional driver on closed course; files in mirror are bigger than they appear; P2Purge is not intended for the operation of nuclear reactors, air traffic control, avionics, medical equipment, or other life-critical systems; etc."
And if you're feeling especially technically competent, Adam still has his FXScript filters available; he mentions these every once in awhile in articles.