Running Totals in a Report Builder Column Chart

I've created a Report Builder Column chart with months as the x-axis
(category) and revenue as the y-axis (value). This correctly displays
the revenue for each month, but I'd like to display a running total of
the revenue for the year.

I'm currently displaying:
Jan $2
Feb $1
Mar $4

I want to display:
Jan $2
Feb $3
Mar $7

I know this is possibly using the RunningTotal formula in Reporting
Services, but I'd like to do this in Report Builder so the users can
change and create their own graphs with running totals. Is there a way to do this in Report Builder?

Thanks.

I have been able to get the running total in a TABLE by right clicking on a field, selecting formula, and inserting the following string:

=Format(RunningValue(Fields!Count.Value,Sum,Nothing),"")

The format statement allows formatting "C" (at the end would produce currency (Dollar sign, etc.), not sure what "" (I didn't want currency).

I would also like to know how to do this in a chart....