All I have seen on the market is the boxy ASUS style adapter
I have no idea of the circuitry within that box, if there is any other than conductors between the two ends.
It sure would seem nice (to me, at least) if there was a cable based adapter that moved the bulky part (if there need be one) away from the tablet body, as use of the device results in the adapter AND the USB device protruding from the tablet.
Sort of along the lines of the Xoom "camera card adapter", except 40 pin ASUS to female USB rather than SD Card slot. Could even have a low profile 40 pin with right angle cable exit for real compact nature.
If something like that exists, please point me in that direction. If not, then perhaps an accessory manufacturer haunting this forum might give it a try?