I would like to pack the content of a directory into an ext4 partition image easily, without mounting a loop device.

Background: I am building a version of Android which will mount system partitions as a loop device for ARM. Though I can create those partition images by hand using loop devices, it is very troublesome. I want to use an sh script to automatically do the work, and without needing to loop mount the dd-created image and use cp -rp. The best is to directly pack the files into an image file.

Question: Is there any simple command-line tools without needing loop mount and root permission that can pack files into an ext4 partition image?