Enterprise Gateway and SSAS Tabular cross-domain

Hi,

Is there a way to allow Power BI to access a SSAS Tabular instance on a different domain to that which the Enterprise gateway is installed on?

So DOMAINONE is the O365 domain and maps to an internal Domain, the Enterprise gateway is installed on a server within DOMAINONE so all good so far. DOMAINTWO has the SSAS Tabular instance on.

I've tried using HTTP msmdpump on DOMAINONE talking to DOMAINTWO as Anonymous but it didn't work (well I could connect using SSMS if I disabled RequireClientAuthentication on the SSAS Tabular server but I wouldn't do that in production).

Any ideas would be appreciated.

Thanks