I have found an other way: the V2DIP2 from FTDI
(http://www.ftdichip.com/Support/Documents/DataSheets/Modules/DS_V2DIP2-32.pdf). It's 2 Host USB Port and an SPI master. Just what I wanted.
I will just have to check how to adapt their exemple HID Device with SPI Master for 2 HID.