Most of those cards only use the PCI connector to balance itself, even that picture you gave of that Vantec Spectrum. If you look at the photo provided by Vantec, there are no electrical traces on the PCI connector, it is only there to secure the fan, so that it doesn't fall down when you move the case around, or if the screw on the back get loose.
If you need one to lock onto a PCI-e slot, just do some modding on that plastic connector, ie. make a notch according to the PCI-e x1 notches and you're good to go.
The power for the fans come from another cable actually that hooks up to the usual 4-pin or 3-pin power connector.