I did not seen the hardware list of K3 but K1 & K2 have USB OTG controller. That means that it can be USB host either. you need just special plug and perhaps kernel dirvers. I am thinking of implementing it too (rather porting/compiling existing driver stack to arm6).
I saw that one guy actually did that for HTC smartphone and described it well, so it is easy to port too kindle.
video:
http://www.engadget.com/2010/06/04/n...-oscilloscope/
sources:
http://sven.killig.de/android/N1/2.2/usb_host/
You will need to buy Mini-AB to female-A to connect any device or even usb hub. (or do it yourself like this guy
http://www.tombom.co.uk/blog/?p=124).