Dear Marko,
One of my Russia customer met the same situstion with you ,below is my suggestion :
1),If you are in the design stage of the pcb, I suggest that you consider design Rigid-Flex PCB , a flex-board could be connected between two boards,which could save cost and greatly enhance reliability.
2) If its produced pcb, and now is in the assembly stage, then I suggest you use the PCI-E98 models connectors, this volume is very small.
Hope above information will help you .
Best Regrds,
Frank