This question led to a new package:
ctanify are useful tools to prepare clean packages to CTAN. Is there also a tool to upload the package from a terminal?
I had now a look on how to code a script to handle the WWW form upload and went with Perl and the
WWW::Mechanize library. The following script allows to upload a contribution to CTAN. The form fields can be provided using
--<name>=<value> or using environment variables, which simplifies the use in Makefiles. I also implemented an interactive mode and error checking for the input.
I uploaded the script itself to CTAN as
See README file on CTAN.