"Open Ended" PCIe Slots... with END CAPS??

The Precision 7875 is specifically listed as having "open ended" PCIe slots (which allow you to put a longer board into a shorter slot). It turns out that I *need* this capability.

The PCIe slots on my main board are indeed open-ended sockets, but they have little "end caps" on them (which, ah, do not come off if you yank on them... even if you yank on them "pretty hard").

Here's a picture of what I'm talking about.  Can somebody please tell me how I get these off so I can use the "open ended" slot feature?  Please???  Thanks for your help: