I wonder if this miniPCIe board by Commel could be included in the stock of PC-Engines or NRG Systems:
It has a Marvell 88SE9125 chipset, which is said to work on APU2 while the Asmedia ASM1061 chipset unfortunately does not. The latter is easier to get a hold on (e.g. Reichelt.de DELOCK 95233) as the Commel MPX-9125 which seems to be made of unobtainium.
Have a nice day,