Hi there 
we hope you had a great start into the new year 
One way is to include the layer in a custom Gerber Output which you can generate using EAGLE, we provide a how-to for that: Exporting a custom Gerber file from EAGLE, please note that we do not support E-Testing or Assembly for this format.
If you have access to Fusion360, we recommend importing your design and create a custom ODB++ Output which supports E-Testing and Assembly.