I don't know what an "exit" program is, but you can use the offset to just adjust the posted code, or use tracking points to control it.
how can I do this in NX 8?
You need to generate the surface contouring operaiton with "Output Contact Data" turned on.
Then (In NX9) when you post, there is an option to output ball center.
In prior releases, you need to modify the post to output ball center instead of tool tip. There is a custom command available for Post Builder.
Of course, it's more complicated than that, but this shoul dget you started.