7250i - Complete hard reset?

I'm selling my old 7250i on eBay, and was wondering if there's any way to
erase everything from the phone. I've tried "Restore factory defaults" but
that leaves all calendar, phone book, and service setting entries.

In the past I've been able to either enter *#7370# (I think) which reset
everything, but that doesn't work on this phone (unless I have the code
wrong). I've also been able to use Nokia PC Suite to erase all data from the
phone. But this has been removed from the content copier in newer versions.

I could take it to get its firmware upgraded to the same version, but it's
over a year old and already has the latest firmware, hence the nokia service
centre want to charge me.

I could leave the battery out of it for a long time. Does anyone have any
idea how long it would take for the backup battery to discharge? My 7110
took about a week.

I could manually go through it and delete everything, but this will take
AGES (I have a LOT of calendar entries) and some settings I can't seem to
delete (Service settings for e.g.).

Any other suggestions of a quick and easy way to delete everything?

Adam