Hi!
There are lot of possible solutions, depending on what tools are available and what level of access you have to these devices:
It is not necessary to run agent under root user to get most of the information, especially on Linux. If you can run agent as non-root user, that could be a solution.
If you can put additional binaries to the device, you can use shell scripts and nxpush command line tool to push data to management server.
You can create scripts on management server (or any other system) to query data from the device and use nxpush or nxapush to push data to management server.
I agree that having "exec" type of DCI origin will simplify configuration in case #3. I have added it as feature request for 1.2.8 release.
Best regards,
Victor