Problems wiring USB-C receptacle
There are several challenges in this project. Here is the connector pinout:




A Type-C receptacle on a USB slave device must provide 5.1k pull-downs on both CC1 and CC2 pins, separate, to inform the attached cable-host that it is a device. Without these pull-downs a Type-C host won't turn its VBUS on, and nothing will ever start.
USB 2 signals must be cross-connected, A6+B6 go to D+, and A7+B7 go to D-. In this case the USB2 the USB2 link will work with both cable orientations.
In a fully-compliant the USB 3 device with Type-C RECEPTACLE the connection should be done to both sides of the connector using separate muxed channels. It is done either in silicon IC inside (like in Microchip USB5926), or using a special multiplexer IC. However, a USB3 device with CAPTIVE CABLE doesn't need to have the USB3 lines duplicated, because the host side will do this function, so the cable will work in both orientations. 
If this is an alternate-mode Type-C device (DisplayPort video converter or something), not only all four SS pairs must be present, but the CC lines must have a PowerDelivery compliant IC to communicate the alternate device parameters and functions. 
and most important, the USB3 signaling is very picky about electrical quality of differential wires. The wire pairs must maintain 90-Ohms differential impedance along the entire link if they are longer than 1-2 cm, otherwise the USB channel will be unable to train it self to sufficiently low error rate, and will disengage. This is likely the most challenging part of this project.


The first two differences between captive cable and full-featured Type-C receptacle must be implemented by you. Items 3 and 4 are likely already built into your device.  

To meet the fifth requirement, you might succeed if you put your new Type-C receptacle at a very short distance, and carefully solder all super-speed links using twisted pairs made of thin magnet (AWG34-38) wires.

And no, VBUS pins are not missing in the dongle, they are combined into one external pad on the little PCB.