It has been a while since my original attempt at upgrading the firmware on my Seagate hard drives housed in my ReadyNAS NV+. Thanks to scostall for his comment on the original post which pointed me in the right direction.
Last week I headed up to Memory Express here in Winnipeg and picked up an IDE to SATA adaptor. It worked like a charm. I pulled the drives out of the NAS (only one at time) hooked up the adaptor to my PC mobo and booted the Seagate firmware ISO. The drives were recognized and the firmware was updated in about 10 seconds. Of course it took about 5 hours to resync each drive into the RAID array, so the whole process took a day or so.
Just a reminder, as scostall warned in his comment, if you are running the drives in a RAID array make sure you only pull one at a time, or otherwise you are risking losing all your data.