Uploading a plugin with multiple nbms

I am trying to put a plugin on the netbeans central repository. The plugin consists of 2 nbm files.

I go to the upload page and it tells me I need to upload a single zip file. I try to use the create ZIP in netbeans and it tells me it will only do it for applications. Do I just put these files in a plain zip, do I need some additional files or am I missing a trick here?

Any advice appreciated.

Regards,

MArk