Well, I solved it a different way using a group account. This turns out to be more flexible.
I converted my DriveHQ account to one with group settings. I then created a group account and shared a folder with that account, giving it add/upload privilege only. I can then get my ftp to go to the group account under the drivehq shares. And the uploaded file can be deleted only through my main account. Brilliant.
I also have the flexibility to pass data back though another folder shared with read only access. Great.