here is a patch to make Location CCK work with the "Multiple field values on a single map" display.
That's how make it work Location CCK after applying the patch:
1) Create a new node type (or use one you already created before)
2) Add a Location CCK field to the node type
3) Configure the field to be multiple
4) go to admin/content/node-type/YOUR_NODE_TYPE/display and select "Multiple field values on a single map" option for your Location CCK field
5) insert a new node of the type you just created and set more than one location (use "Add another item" button).
6) Save the node and you will see only one map for that node showing as many markers as many locations you provided for that node
Please note that you will need to clear the cache (admin/settings/performance) after applying the patch.
Please try it out and give feedback.