Custom.lkp file cannot be added to the project. To use custom linker actions, all you have to do is create a 'custom.lkp' file in your project root folder and define your custom linker operations as explained in help (Press F1 in designer and then search for 'custom lkp', you should get the details). Or else let me know, I will explain.
Thanks for the response, I had already implemented this. I notice
in the link file it does not "directly" tell a user where stack starts,
just end of RAM. Label terminology could be improved.