Not sure about the 19 GPU.
you can get these PCIE 1x cards that can run 4 risers.
Have seen them, but never tried one.
I've used quite a few of the 4-in-1 Risers. They work perfectly. They sit tight in the slot, and no performance problems at all.
I have MATX boards with only 3 PCI-E running 8 GPUs.