I don't think its possible, judging on the people around me at the ground and their usage, probably half the people in the ground go on their phones. Lets play it safe even with 5,000 people using the WIFI at one time would still be impossible bandwith. Imagine 5,000 people all rolling up and using the WIFI at your house, it's impossible.
The mobile networks themselves obviously have proven it's impossible because like now, they cannot cope with the amount of data. Data used is chargable by the provider especially in masses, the club isn't going to pay for thousands of pounds+ worth of data and offer Wifi out for free. They've probably just left it to the phone networks to sort out.