I'm not sure that I understand exactly what you need, but there are several variables that can be used in external launch configurations.
In your description, most likely to put $ {resource_loc} in the field "Working directory:".
From the description:
Returns the absolute path to the resource file system. The target resource is the selected resource if no arguments are specified, or the resource identified by the relative path of the workspace.
Alternatively, $ {container_loc} might be more appropriate if you need to run in a directory:
Returns the absolute file system path to the resource container. The target resource is the selected resource if no arguments are specified, or the resource identified by the relative path of the workspace.
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