Here's what I would like: var xyz = ( \t )
[snip]
Here are my current indenation rules, could anyone help me get what I'm looking for, or have I been looking in the wrong place?
What you're actually looking for is a snippet, not indentation regex. I would also suggest using Thomas Aylott's refactored JavaScript bundle, currently in the Review section of the repository. It adds scopes for the various braces that makes this much simpler to implement (among many other reasons for using it).
The basic pattern is the same as the snippet in the HTML bundle named "Special: Return Inside Empty Open / Close Tags". It relies on the meta.scope.between-tag-pair selector, which is defined in the language grammar. The content of the snippet for JavaScript is exactly the same, you'll just need to adjust the scope selector according to the particular flavour of JavaScript.tmbundle you are using.
I've attached my own take on it, which also applies to array literals ( [] ).
Hope this helps, Daniel