So,
if(IsInEurope(Customer.Country) || IpAnalyzer.IsInEurope(visitor.Ip))
{
//Enable something
}
Should do it. But fallback method should be implemented, took me 3 minutes of reading documentation + googling.
Between all those tax regulation differences, I think this one is mostly straightforward for handling global payments.
Ps. Don't forget to encrypt your actual data, I think you will be amazed at what needs to happen for selling in EU ;)