I tried a bit but couldn't get it to work with your server as end-point.

But to be honest, I'm also not sure this is worth the trouble: It has been a very long time since I last worked with and contributed to Roundup, so getting back into Roundup's code requires quite a bit of work for me now.
I can't believe that it's hard to rewrite my original patch to work with a more recent version of the `xmlrpc` API. So if there is real interest, I'm sure someone with a current interest into the project will be able to fill in the missing bits.