VoiceAttack can compile C#.
You can add an inline function action("Other >", "Advanced", "Execute an Inline Function", "C# Code") and replace the default template with the second code block I posted. Make sure to check the "Wait for the inline function to finish before continuing" option(otherwise the function is executed asynchronously, and if the TTS action runs before the variable is set, it'll just speak "Not Set"; I.E. a race condition may occur).
If you want more delay between digits, try ", "(a comma and a space character) instead of just a space.
You can also combine this with SSML for more granular control over TTS(tokens are essentially functions, and once they're parsed they are replaced by the output of their execution, so they can be used wherever literal text would be, in fields that parse them).