Perhaps the solution is not to give all users all IP addresses, but only a small portion of them, making such an attack harder to carry out. However, this method has limitations—users will be restricted in terms of locations, and problems may arise if, by chance, none of the IP addresses provided to a user work for them.
Some competitor VPN's don't give every user access to all its bridges. Despite this, they offer unrestricted locations to users, and their service successfully evades restrictions.