It's a [Removed - Language] backward solution, but it works. Go through the normal process of adding an offline loan account. Once you get to the Your Loan Reminder window, click "Back" until you get to the Add Account window again. This time, select Other Assets & Liabilities and click through the windows to set up the liability until you get to the window with "Do you have a loan against this liability?". Select "No", click "Next", then "Finish". The new loan account will be there along with the new liability account. You can then delete the liability account.
Maybe one of these years Quicken will get around to creating a fix for this annoying issue.
[Edited - Readability]
