I had made a small plugin exporter/importer before for other tool.
My solution is to make a client tool to export plugin by these steps:
1. get the plugins list (folder)
2. pop up a gui to let user select which plugin (folder) need to be exported
3. zip plugin (folder), save it to other location.
- In your case, you can save it to your server.
So that you don't need to collect/maintain these plugins.
Since zipping is handled by client tool, server can unzip it and get data correctly.