I'm going to give you a very drastic solution that I WOULD NOT DO. But it is a valid option...

Alright, PCIe connectors have a common part which is the first part that is the pins for power. The rest, which is where there are different "sizes", are the data lines. The more lines, the more bandwidth, and the faster the data transfer speed.

Now comes the "destroyer" DIY... Well, if you dare, you can cut the stop that is in the back that makes the PCI card not fit. If you decide, you have to do it very carefully so as not to damage any pin of the connector...

Anyway, I'm giving you a tip that I would never do on my main board...