How to add/insert an item into an ObservableArray at a certain position with Knockout.js

You should be able to use the native JavaScript splice method –

viewModel.SomeItems.splice(2,0,someNewItem);

Docs here – https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/splice

Example here (not Knockout specific) – How to insert an item into an array at a specific index?

From the Knockout docs –

For functions that modify the contents of the array, such as push and
splice, KO’s methods automatically trigger the dependency tracking
mechanism so that all registered listeners are notified of the change,
and your UI is automatically updated.