If you have ip mobility enabled, that throws everything out the window, and there is no quick easy solution.
"Even" vlan membership is only calculated locally, so users would not be put into the same VLAN as they were before if they end up on a different controller. There are a number of ways to slice this, but a single large VLAN that all the controllers are trunked to is the best solution ultimately. ip mobility can be complex, and it also complicates troubleshooting because you are not always aware what AP a user is connected to, if its traffic is tunneled back to another controller. It also does not make it easy to add subnets once your pool is
If you use a single large VLAN with broadcast filtering at the Virtual AP level, all of those problems go away...as long as you have a layer 3 switch that can accomodate all of those mac addresses, you should be good to go...