It is possible to modify the ACL on the settings files (during installation) to make them writeable for standard users. This is commonly used, though very undesirable. See issue 14 here in a list of common design problems in MSI files: How do I avoid common design flaws in my WiX / MSI deployment solution?
I doubt Installshield LE has any features for this ACL modification. WiX does, as does the commercial edition of Installshield and Advanced Installer. There are other tools as well that may support it.
Another "solution" that I don't recommend, but that is still used by many: How do I force my .NET application to run as administrator? I suppose this is effectively what you are doing? See this answer as well for an important note (it is a different answer from the same "thread").
The real solution is to re-design your application to not store settings files in the application installation directory, but rather store your settings in HKCU in the registry, or in a settings file stored in the user profile. Regular users can obviously write to these locations.
Not 100% the same, but very related. An answer with a list of options to allow an application to write to HKLM in the registry: Per Machine App Registration. Recommended read / skim.