You should be able to do this with a BRString. I tested the below and it was successful:
WFProfile=WFProfileName, WFScenario=ScenarioName, WFTime=XFBR(RuleName,GetWorkflowStartTime)
In a Dashbaord XFBRString BR:
If (args.FunctionName.Equals("RuleName", StringComparison.InvariantCultureIgnoreCase)) Then
Dim scenarioId As Integer = BRApi.Finance.Members.GetMemberId(si, DimType.Scenario.Id, "ScenarioName")
Dim wfStartTime As Integer = brapi.Finance.Scenario.GetWorkflowStartTime(si, scenarioId)
Dim wfStartYear As Integer = BRApi.Finance.Time.GetYearFromId(si, wfStartTime)
Return BRApi.Finance.Time.GetNameFromId(si, wfStartYear)
End If
You can make this more dynamic by passing in the scenario to the BR using a parameter, variable, etc, but did not for the simple purpose of showing how it could work.