Prevent a USB external hard drive from sleeping

Does anyone know if there is an elegant way to tell an external usb drive not to spin down after a period of inactivity? I've seen cron based solutions that write a file every minute, but nothing that smells of nice unixey elegance. There must be a hdparm, or scsi command that I can issue (usb drives are accessed via the sd driver in OpenBSD) to the drive to tell it to not sleep. I'm afraid that this is probably a *feature* built into the controller in the enclosure, and as such not much can change it aside from ripping the drive out of it's enclosure and plopping it directly in the machine, but I figured I would ask, on the off chance. Ideally, I'm looking for an OpenBSD solution, but I know there are others out there w/the same problem so any solutions will be considered for the answer.