You can't because the VPN users always have to connect to the interface address (well, I suppose you could configure a load balancing cluster with one member...),
However you can simply do the opposite, i.e. let your vpn client users connect to 1.1.1.1 and use 1.1.1.2 to NAT your internal users.
nat (inside) 1 0.0.0.0 0.0.0.0
global (outside) 1 1.1.1.2