Go to home depot, get a solid switchplate (no holes)..
Get one of the back mounting plates, take the jacks out, use it as a template to trace the opening you need, then carefully drill and file it out to look all slick.. Then spraypaint it whatever color you want.. Then hack your extension cable onto the short little mobo jumper the back mounting plate has (black to black, yellow to yellow, green to green, red to red) - it'll be fine for keyboard/mouse, the hack wont impair the little bandwidth they need.
The do sell steel and metal plates, but plastic would be easier to work with.
It's how I've put front/side/wherever usb ports on plenty of PCs over the years, with a little careful work with a small file, it'll look like it was machined that way.