all it would take is one of the said company people to use a dialup service, one of the many that are available and then access your site via that dialup which will be an IP address not in the same range as the company internet.
They can also use one of the thousands of free proxyservers that allow the internet users to browse other site without being hindered.
Both methods work fine for instances where you are unable to access a website because your IP address or DNSname has been barred by that site.
So save your self the bother and get on with your site, your competitors have better things to worry about than spend all their time looking at your site, so why are you worrying?