Crystal reports running totals in Crosstab

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CrystalReports

Hi,
I have a crosstab:rows is date coulumn are total and mode(mode1,mode2...)
also have function to run Cumulative total or running total.
Report do correct calculation in the running total but if one day have no value so the running total for that column (ex, mode2) will show 0 for every day where is no value for that day. But if any other date after the MODE2 has a value the report will show the correct running total.
The problem is we do not want to see 0 in running total rather will see the previous cumulative running totals.
Thanks for any advice or any formula to correct this issue.
Thanks,
ex:
01//01/2011 1 2 3
running total:1 2 3
01/02/2011 5 0 2
running total:6 0 5
01/03/2011 :7 1 5
running total:13 5 10

on 01/02 i want to see the running total as 4 rather than 0