I'm not quite sure I understand the question. I'm guessing that what is displayed in the sidebar is a list of GoogleMarkers, each located at some specific (unique) location. Instead of displaying the ID for the marker in the sidebar you want some other value displayed? You are not using the location name to identify the marker as it is not unique.
The problem is that the sidebar is in fact an HTML table. Unlike select tags in HTML tables don't have visible and hidden values, so it is not directly possible to set some hidden value that works as a unique identifier. In the next version of the sidebar the default display text
for overlays in the sidebar will be the name property of the respective
overlay options. This should give some more flexibility to display
overlays with non-unique names.
This of course does not solve your problem now, but what you can do is to write your own postback command and set the unique id as the argument. To make your markers' names unique you can add a counter after the name when you add them to the overlay collection (ex. "Drug store 1", "Drug store 2" etc).