SQL Express and Report Builder Licensing - Terminal Services

Hi Guys

I have an RDS 2012 R2 environment and have had a request to install SQL Express and Report Builder on one of the servers. Do you have any ideas if I can install this in a Terminal server environment and publish report builder as a published remote app. From a technical point of view it works fine. Just want to make sure I am compliant with MS and dont need to purchase licenses. 

Thanks!