libguestfs API: passing custom arguments to file function

[Wenzel]

libguestfs API allows you to call the file command from the appliance to identify a file type.

however it is not possible to specify the parameters.
we would like to query only the mime type:

file -i /path/to/file

The current solution is to call g.command() but it relies on the binaries available on the current analyzed disk.
And of course it doesn't work on Windows.