Hi,
If you're assigning addresses to the VPN clients from a local pool on the ASA, you can assign a specific IP to a specific user all the time.
Let's say you have a user ''cisco''
username cisco attributes
vpn-framed-ip-address Enter the IP address and the net mask to be assigned
to the client
You use the command ''vpn-framed-ip-address'' under the attributes for the user.
Hope it helps.
Federico.