Inspections of product are supposed to be performed to confirm conformance to specification and to control the process, before non-conforming product is produced (The ISO requirements are about prevention, not detection, remember?).
Is it correct and appropriate to use process capability to define the frequency of inspections to detect any adverse trends in capability (common and special cause) which can cause defects. Therefore your inspections should be performed at a frequency to detect trends and shut the process down/reset the process or some other action.
Your auditor is somewhat on the right path, because it's linked with the use of statistical techniques, hence frequency. So, stating you check one in 10 parts or every 30 minutes of production isn't really going to fly (which is what Jan's talking about - when you can get to it.....kind of thing)