Is there a way? Well, in theory you can still use it inside the case, as the 5v version came with a USB adapter cable no? But will involve plugging into a USB power source to power it and then routing that USB cable into the case. Which is unlikely what you want to do I'd imagine.
Personally, if you haven't opened it already, just sent it back to retailer saying it's the wrong one and you were after the normal 12v PWM version (or whichever version you were actually after). As without some heavy modding to the power coming through the PWM headers, they will drop 12v through to your A12x25. Either killing the fan, and/or the fan header, and if you get really unlucky, maybe more.
So USB routed into the case for the fan, or return are you best bets here I think.
Or, use it for something else other than your case. I haven't got a 3D printer, or I'd have printed out a copy of that Noctua Desk Fan design and put it in to use as a (hopefully, cool and quiet) desk fan. Or used it inside enclosure that's housing a NAS.