How to Apply a code in a RunningValue expression in SSRS

Question

I have the following conundrum:

I made a code inside my report that basically accumulate value, here:

Dim number as Double 

Function Accumulate(ByVal value as Double) As Double

number=number + value

Return number

End Function

And I made a calculated field like this:

Code.Accumulate(Fields!MyField.Value)

Now, the field Myfield It's a number so the Function will run smoothly, the problem is the following expression I want to apply the code:

=FormatNumber(RunningValue(Fields!MyOtherField.Value, Sum,"Dataset"), 2)

I can't because as you see it have an aggregate function so I can't create a calculated field with this expression.

Is there any way I can apply my code to this expression or I have to create a code that does the same as this expression?

If you need more info, ask away and I will edit my original thread.