SSRS 2016 Mobile Reports - Using Expressions

We have started working on SSRS 2016 Mobile Reports. The problem we faced is that it does not support writing expressions.

I will explain...

In SSRS 2016 paginated reports, we are able to write the following expression in any of a tabular/matrix cell or chart level:

SUM(X)/SUM(Y) as this is a weighted ratio that should be calculated correctly at each aggregate level.

Now with SSRS 2016 mobile reports, the only way to fetch this information is through datasets. writing SUM(X)/SUM(Y) in a calculated column in a dataset query means that when this data is aggregated in any chart in mobile reports it will be evaluated as SUM(SUM(X)/SUM(Y)) and this leads to incorrect result.

Note we are reading directly from a DW

Any ideas how to get around this issue without having to use OLAP cube (i.e. directly from DW) ??

Luai7