Another option would be to cut a hole in the back of the built-in directly
over the box, and add an extender ring to the box to bring it flush with the
inside surface of the built-in. Then attach the cover plate of your choice.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

That's what the problem is...there are two bookshelf components that
join each other right over the place where the outlet or junction box
is.

I think my fix for this would be to cut a new hold in the back of the
built-in and through the wall, Then find the wires that lead to the
old junction box and snip them (with the power shut off of course).
Then re-route new wires to the new j-box in the back of my built-in.