Is it possible?
1. Write to /cache/recovery/command file
2. Reboot device into recovery mode
3. Get how much free space in /system
4. Read file from /system
Reading and writing to files is possible with the File object.
These folders are not accessible for unrooted phones.
A reboot method can be added to the phone library easily.
While searching for more information I did find a way to run shell commands. Not sure that you will be able to run those commands as super user though.
I will add it to the list...