Unfortunately there isn't an one click method to copy an existing static as an activator, but it's not very difficult either.

What you simply have to do is that you have to create a new activator and assign it the same mesh (Add Art File) as the original static has. This is complicated by the fact that the vanilla and Tamriel Data assets are packed into BSAs so you can't simply select them from the file explorer, but you can unpack the BSAs using BSA Unpacker, or alternatively, there's a workaround that you can use:

1) Find the static you want to turn into an activator, and make note of what mesh it uses (in this case it's sky/f//sky_flora_tr_b_03_01.nif)

2) Create a new activator by switching to the activator list, right clicking and selecting New. Give it a name.

3) Click on Add Art File. A file explorer opens in the "meshes" folder of your Data Files folder. Navigate to the folder where the mesh for your activator is supposed to be (so in my case sky/f). If these folders don't exist in your folder structure, create them.

4) Copy any .nif file to the folderand rename it so it shares the same name with the mesh you want to use (so sky_flora_tr_b_03_01.nif), select it and click OK. Now you have an activator that has the same mesh as the static you want to use.

To clean up, you should delete that dummy file from the folder, but the CS actually gives precedence to the assets from the BSAs, so you don't strictly have to do that.

Hope this helps!