I had a bit of a think. I'm thinking that the blocking is done on the basis of the domain name, not the IP address, because the morons who implement this stuff didn't think of blocking domain name *and* IP address, so I found a neat way round it.
First, I edited my hosts file (in /etc/hosts). I invented a domain name that doesn't exist called "mynewmagicwand.com". Because it doesn't exist, it won't be on any suppression list. Also, you can't access it, because it doesn't exist. But I told my hosts file that data.mynewmagicwand.com had the ip address of my admin computer.
Then I accessed it via the Hotel Disney Wifi, and it worked fine.
Let's hope that the kids don't find out about this simple idea.
So now you know how to get round the blocking mechanism in the Eurodisney hotel, and it'll probably work for anywhere else. The same idea will work for a Windows computer, if you can work out where it keeps its hosts file; I seem to remember that Windows puts is somewhere quite obscure, but I imagine that Google could tell you where.
Apple users - you're on your own.
Should I tell the hotel people here about this little bit of magic? They told me that they encounter this problem all the time.