Support ADFS Forms authentication for SSRS server

We use ADFS 3.0/WAP forms authentication (non-claims KCD) to provide an SSO experience for our users accessing internal apps outside the company firewall without VPN. It would be nice if the SSRS portion of the Power BI app would allow authentication this way like Office apps do. We can avoid the problem by creating another endpoint on the firewall allowing NTLM authentication but then we end up with 2 SSRS URLs (one for accessing via browser that has SSO experience and one for the Power BI app).