Flexible PCIe riser. The longest single riser you can get is usually ~ 4" (11cm), and I think if I positioned the board and GXF card carefully that would *just* about be long enough, but ideally I'd have something > 15cm in length to give me some flexibility in positioning (or a combination of multiple risers to have the same effect, of course ).
I'd love to have the time and money to make something like this, but frankly I'd probably need a trusting customer who'd commission the build and pay up front to make it viable. And building PCs is no way to make money...