Basically I agree with your opinion, but as the target could run on linux and windows machines as well and because the vulnerability is simple OS command execution the solution could be complex. The payload must be splited to several parts (because of the GET request length limitation), the parts must be concatenated through OS command execution (echo 'xxx' >> targetfile) and after that it must be executed and of course the path to the temporary file and the execution method also depends on the target OS. So it is possible but not as easy as just execute one simple OS command. I will try and create an exploit module for your needs but I'm not sure if I will have enough time and access to the vulnerable environment to perform tests. I suggest to leave this module as a simple one OS command execution aux module now and I will try to create a new exploit module later. What do you think?