|There is no such adapter, to my knowledge. The extra pin is just a second ground and is not needed. |
You can remove all the wires from the plastic connector and connect them individually. If you look carefully you may be able to see a locking tang on each wire terminal. You need to depress that tang in order to remove the terminal from the plactic connector.
BTW, if your motherboard happens to be a Gigabyte brand I believe they STILL use a different pattern for the wires. That means you must perform the described operation anyway. Even if the connector did fit.
Below is a link showing the wiring connections. You can also use wire cutters to cut the plastic connector away from the terminals.