There doesn't appear to be a solution within the domain of bordered text.

The work-around solution I have come up with is to 1. adjust the tab of the un-bulleted bordered style to 0.25 inch, and 2. create an Autotext entry of the following series: tab, lower case o, tab.

The "o" is formatted to Berlin Sans FB, which has a constant-width stroke, and raised a point.

Thus, replacing the second-level bullet style, a paragraph in the un-bulleted style is preceded by this entry.