Alias for multiple instances on a SQL Server
It's a little tricky with multiple IP addresses and different ports when configuring SQL Server. The most important bit, is that the whole configuration has to be done with the SQL Server Configuration Manager.


Open up the SQL Server Configuration Manager with Runas Administrator...
Navigate through the SQL Server Network Configuration branch and you should find two sub-branches for ...
a. Protocols for NAMED_INSTANCE_1
b. Protocols for NAMED_INSTANCE_2  


Repeat the following steps for each instance:  


Click on the Protocols for NAMED_INSTANCE_n branch and in the right pane right-click on the TCP/IP Protocol Name entry.  
Open up the properties.
In the Protocol register verify the following:
a. Enabled = Yes
b. Listen All = No  
Switch to the IP Addresses register
You should find sections in the form of IPn for each of your IP addresses 10.10.1.1 and 10.10.1.2. This is the tricky bit: You are already in an instance and want to configure only one IP address for this instance.
In the IPn section corresponding to the IP address for this instance check the following:
a. Active = Yes
b. Enabled = Yes
c. IP Address = 10.1.0.n
d. TCP Dynamic Ports = leave empty
e. TCP Port = 1433  
Scroll down to the IPAll section
Verify the following:
a. TCP Dynamic Ports = leave empty
b. TCP Port = leave empty  
In all other IPn sections ensure the following:
a. Enabled = Yes
b. Active = No (unless you want to communicate with the instance via the IP configuration settings in the section).  


Repeat from step 3. for each instance.

You have to restart the instance and then it will only pick up on the IP address and port configured.

We have SQL Servers with up to 10 instances configured this way, but we leave the port at 1433 so that each instance will pick up on the default port. This allows for easier firewall configuration.

Good luck.