Question / request for pre-grouping keys in Aggregate operation

[whutjs]

Hi, we are using substrait & velox to build an OLAP execution engine. Besides specify the grouping keys of aggregation, we can also specify the pre-grouping keys in velox. Pre-grouping keys are a subset of the grouping keys on which the input is clustered, i.e. identical sets of values for these keys always appear next to each other. We'd like to be able to specify the pre-grouping keys in substrait but we fail to find a way to do that. Does substrait support specify the pre-grouping keys of aggregation? If not, will it be supported?