Once you open up the boxes and look it will be obvious how to do what
you want to do. Look, draw, think, wire. Preferably in that order.

As others have pointed out that doesn't make it the best solution or
to code.

Aren't you going to end up with lighting and branch circuits on the
same breaker? Pretty sure that's against code, you ought to look it
up. For that matter, your extension cord across the ceiling is
probably wrong. You really ought to run a new circuit from the panel
to your computer area, and this is not that hard or expensive to do.