3GXMR installation - orientation?

[HindandSeek]

Bought a used, never flown t-rex 450 super combo when I was just starting out (3 months ago) that came with the 3GXMR.(the seller claimed he paid over $450 for this gyro, but that's another story)
It is required to be mounted face down, but all the cables are routed (very nicely by a professional to the top, so mounting it under the tail won't be possible. If I mount it on top of the tail case, half of it would have to stick out because of the button on it, and I'm afraid it will vibrate all over the place.

Any ideas? (apart from buying a new gyro, which I'll probably have to do eventually, given the 3GX reputation)