I too switched from DropBox to Copy because of its great Linux integration.
I have tried their software CudaDrive on Windows which lets you access files in the cloud without having to sync them to your local device.
I achieved what you are trying to do on Suse and *ubuntus 15.04 and 15.10 by using third party software called StorageMadeEasy. You may not wish to use a third party proprietary piece of software and certainly askubuntu mods dislike this solution but it meets every criteria in your question.
They provide a deb which once installed allows you to map your copy cloud as a network drive.
Steps:
- Create a free account with StorageMadeEasy and link your copy account
to it.
- Download and install the deb (or relevant package for other distros)
from https://storagemadeeasy.com/LinuxDrive/
- Create an empty folder that you can mount the copy folder to Search
SME from the menu, this will bring up three options, choose SME
client.
- Sign in with your StorageMadeEasy account
- Select the previously created empty folder
- Click the big Mount button and wait for the success popup.
- You can now browse and edit your copy.com files as if they were
local.
Alternatively with the StorageMadeEasy account you can access the copy.com folder using WebDAV. I'm afraid I haven't experience with this but this option is applicable to every linux distro whether a package exists or not.
I'm not associated with SME or Barracuda in any way other than being a customer.