Hi David,
We don’t (yet) officially support other languages or making custom calls to the client, but I can let you in on a secret bit; the IDL (the argument encoding) is normally prefixed by DIDL as the magic bits. The encoding is not yet ready to open source, so if you want to pass in data you’d have to reverse engineer it yourself. In the meantime, an empty field should be encoded as DIDL\0\0. Your Motoko code will not get any arguments.
Hope this helps!