qemu-img compress image from stdin / gunzip

because of low space i would like to gunzip a zipped "glance image-download" and compress it with qemu-img to a "qcow2" formatted file. tried this: gunzip -c file.gz |qemu-img convert -f raw /dev/stdin -O qcow2 file.qcow2 but it fails with: qemu-img: Could not open '/dev/stdin': Could not refresh total sector count: Illegal seek Any idea if this is at all possible?