Hum, I would not call it a very good solution. It was not possible to run calibre without Qt, so I compiled it with Qt. My initial problem was flash usage: I wanted to install everything on a small USB Stick. Since I do not own a Sheevaplug (but a Seagate DockStar, which is in fact a docking station for Harddisks) i chose to buy a Seagate harddisk and install the system on that drive.
Since it would take some time (probably several days or because of low RAM [128MB] even weeks) to compile Qt on the device itself, I chose to use distcc (
http://www.gentoo.org/doc/en/distcc.xml) and effectively compile it on my desktop machine.