Use a uniform IP address for VPN access over the Intranet ???

Use a uniform IP address for VPN access over the Intranet ??? -- Linux Enterprise Application-Linux server application information. For details, refer to the following section. Assume there is a VPN Server (RedHat Linux AS4) Dual Nic
The Internet IP address of this server is: 207.68.178.61
Intranet IP Address: 192.168.0.1
Currently, in VPN mode, a user dials a VPN Server over a public network and assigns an intranet IP address (which may be 192.168.0.2) to each user ),
The assigned Intranet IP address varies with each user. Then, the user can access the Intranet through the assigned IP address.
However, it is not easy to allocate an IP address pool in advance, which reduces the number of IP addresses of Intranet users.
Now we want to enable users to dial in to the VPN Server through the public network. No matter how many users dial in, they can use an intranet IP address (such as 192.168.0.100) to access the Intranet.
How do you implement it ????
Thank you !!