How to install card in expansion slot on Aspire ATC-710-UR56?

I want to add an expansion card with several additional USB ports. It has both a PCI-E and a PCI-16 slot. Acer has told me that I can add a card with up to 6 additional USB 3.0 ports.

However, the bay access to the rear of the PC is a problem. Instead of removal bay covers (in the past, these have been held in place by screws), the covers are affixed by metal tabs to the chassis. There is a spring-held clip that seems like maybe it could hold the end of a card so that the row of ports would be open to the rear (and thus accessible), but how this would work is unclear.

I don't know if this adequately explains the situation, but does this seem familiar to anyone who has tried to add an expansion accessory to a new PC like this recently?

Basically, since I cannot unscrew the covers over the rear bay openings, I think it would be necessary to cut or file through the metal tabs holding the covers to the chassis. Is the PC owner actually expected to do this to utilize an expansion slot? If so, what's the best way to do this?