Jake, while this may not be officially supported, and I've never done this myself, nor heard of it being done by anyone else....I can't think of any reasons why it WOULDN'T work. Naturally though, as soon as you insert any sort of coupling device, you will see some amount of signal attenuation from that device. Make sure to take that into consideration.
I see what you're saying about the cables and box fitment. I don't recall ever seeing a 90-degree adapter, so you might be on your own for this one.