[bofh23]

There’s a nice photo of an open back PCIe x1 connector here:

File:PCIe J1900 SoC ITX Mainboard IMG 1820.JPG - Wikipedia https://en.wikipedia.org/wiki/File:PCIe_J1900_SoC_ITX_Mainbo...

[loeg]

You can also literally just file down the plastic on any “closed” socket to make it open.

[mmis1000]

Only work if your motherboard don't have other items (socket, capacitor... etc) in that area.