Data Grids - adding dimension member rows dynamically

Summary:

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I'm looking for a simple way to allow users to add account dimension member rows to a data form when inputting data.

We already have a a solution to allow users to add account rows using a business rule and a right-click menu. This currently works where all the rows are included on the form layout in design view but with suppression applied on zero balances. Then, the rule simply writes a value of '1' to the BegBalance period member for the account that end user wishes to add, and this brings the row out of suppression so it shows on the form for normal data entry. What the user sees is the row being added to the form but in actual