Adding items to a string array with an unconventional name

I am trying to name an array after the value from another variable, and then add multiple items to it by referring to it with the value from mentioned variable.

For example, I can do the following:

PS C:\Users\Administrator> $IP_Address = "100.100.100.5"
PS C:\Users\Administrator> New-Variable -Name $IP_Address
PS C:\Users\Administrator> Set-Variable -Name $IP_Address -Value "Test string"
PS C:\Users\Administrator> Get-Variable -Name 100.100.100.5

Name                           Value
----                           -----
100.100.100.5                  Test string


PS C:\Users\Administrator> ${100.100.100.5}
Test string

But I cannot figure out how to add items into the variable ${100.100.100.5} by refering to it using $IP_Address.