Nope, sorry, no can do that!
You would need the USB port on the primer to be able to act as USB host or OTG (on the go) on both.
USB on the STM32 is device only, that is can only be peripheral device to a PC or something that supports USB host or OTG.
Better use the SPI interface on the extension connector (I assume it's a Primer 1); can actually be faster than USB full speed; alternative you can use USART if you are more familiar with it.
