Strokes in InDesign don't have the flexibility they do in more purely graphic apps. (Well, you can often get to the same result, but the tools tend to be clumsy.)
If drawing a line around three sides of a frame isn't the right solution, there may not be a much better one. You could try this: put a stroke around all four sides. Use a graphic frame to mask one side (probably with a white/Paper fill). Then, if you need that stroke to appear, make the masking rectangle disappear. You can do that by either putting the masking element on a separate layer (which can then be turned off), or by using a defined fill color you can globally set to "None." The latter could be grouped with the framed object and copied or moved around, so that might be better.
Best I can come up with from a simple description of your need and the "maybe" nature of the change.