From Help in Exchange System Manager, under multiple SMTP Virtual Servers:
Create Additional SMTP Virtual Servers
To create a new SMTP virtual server:
Note By default the assigned IP address is (All Unassigned), which means the virtual server will use all available IP addresses not already used by the selected TCP port. This includes 127.0.0.1, the default IP address for the local host.
Start System Manager: On the Start menu, point to Programs, point to Microsoft Exchange, and then click System Manager.
Navigate to SMTP.
Servers
Server
Protocols
SMTP
Right-click SMTP, point to New, then click SMTP Virtual Server.
Complete the New SMTP Virtual Server Wizard.
When you select an IP address, remember that the IP address/TCP port combination must be unique on every SMTP virtual server. The recommended TCP port is 25, the SMTP standard TCP port. More than one virtual server can use the same TCP port, provided they are configured with different IP addresses.
Note If the SMTP virtual server will be using a new IP address, you will have to first configure that new IP address before it can be used by Exchange.
If the default startup setting for SMTP Service is set to Automatic, the new SMTP virtual server will start on its own. If the virtual server doesn't start, it may be because you selected an IP address/TCP port combination that is already in use.
Configure the new SMTP virtual server.
Note If you do configure an IP address/TCP port combination that is already in use, a pop-up window will alert you. Select a TCP port that isn't being used by another virtual server on that IP address.
Looks like you can't use the same IP, but it's simple enough to add an IP to acomputer (Go into TCP/IP properties, where it shows the address, go to advanced and add one). Hope this helps!